For reasons having everything to do with Dust to Dust, I started thinking about how a character in Mage would conceal a weapon from various levels of searching. While I don't have specific plans along these lines in my own Mage game, characters might very well want to sneak a weapon into a meeting, and magic seems like a pretty good tool to accomplish that task. (Aside from a spell's ability to deal Aggravated damage after a certain point, Weaponry and Firearms offer larger dice pools than direct damage spells in many circumstances, assuming you've bought skills along those lines... and you don't make Paradox rolls to fire a gun under most circumstances.)
Some Arcana have self-evident ways to accomplish this goal, while others require more thought or combination with other Arcana. I seriously doubt that any of these will be Covert, except for (arguably) Mind.
Matter is the most self-evident of all. Three dots: Transmute Earth! Yay, that metal weapon is now something socially acceptable to carry, such as a bracelet or (perhaps rather bulky) necklace. Or, if you're feeling saucy, four dots: Lesser Transmogrification turns your 9mm into the water in your bottle, or the shampoo that the TSA is going to confiscate anyway.
Space is almost as self-evident, though the core book doesn't have anything quite right. I would call this a completely reasonable three-dot Vulgar effect - a kind of micro-version of Pocket Realm and Safe Keeping. This is strongly within Space's theme, so I'd want them to handle this task about as easily as Matter did.
Prime plays a secondary but important role in hiding weapons: once you've cast the spell to hide the weapon, you need to hide the spell that hides the weapon, at least if you're going to be around other mages. Prime 2's Transform Aura is either the right way to do this, or a basis for the right way to do this.
To handle the primary function of hiding the weapon with Prime, Phantasm (Prime 3) is probably your go-to effect, unless the disguise needs to stand up to extended rough handling. If it does, then use Prime 4's Phantasmal Weapon - either tweak the spell to create a durable masking illusion, or ditch the mundane weapon and fight with a Phantasmal Weapon.
Life doesn't bother. Life gives the mage claws and superstrength. If you're not satisfied with that, though, try Fantasia (Life 5) - hollow out a portion of your body and hide the weapon there. It's ridiculous, but this is just not Life's strong suit. Honing the Form (Life 3) can increase the caster's Dexterity by a large amount, helping his Dex + Larceny roll for Sleight of Hand - other than claws, this is Life's best course that I can see.
Death handles this task sort of clumsily, but decisively. Ghostly Object (Death 3), cast on a weapon you don't need in day-to-day life, makes it a Twilight object. Touch of the Grave (Death 2) makes it somewhat fragile, but otherwise usable as per normal.
Spirit has a solution that is much like Death's: Cast Rouse Spirit (Spirit 3) on a weapon, followed with some finagling to get the weapon into an appropriate location in Twilight. Then cast Reaching (also Spirit 3) to use that weapon. This is intensive in advance planning and is Vulgar, but (unless I misunderstand the interactions of Twilight objects and non-Twilight opponents) pretty effective.
Mind has two really fun ways to solve this problem. The first is that even when a mage has no dots in Larceny and a rather poor Dexterity, the observer doing the searching is going to have a tough time if you Befuddle (Mind 4 - and Covert!) him and significantly reduce his Wits or Composure. Breach the Vault of Memory (Mind 4) is sort of a brute-force way to make him forget seeing a weapon, but it too is Covert. The graceful way to do this is to never get searched, thanks to Emotional Urging (Mind 2, still Covert), or to trick the senses of the searcher with Impostor (Mind 3, and yeah, still Covert - you want at least two successes, to cover sight and touch; third priority goes to sound).
Forces is (as you might expect) unsubtle here. Invisible Object (Forces 2) explains itself, but you might still have to worry about getting patted down - Invisible Object won't do anything for its volume. The obvious followup to handle that is Telekinesis (Forces 3) to tow it behind you; the classy variation on that theme is Autonomous Servant (Forces 3 and Mind 1), to carry the weapon and offer it when needed.
The one thing Forces does better than any other Arcana in this general theme is foiling mechanical weapon detection (though Lesser Transmogrification in Matter 4 certainly makes a weapon stop being metal) - better in that the benefit applies to the whole party's weapons. If Science is your thing, use Transmission (Forces 2 - Covert!) to send false data to the metal detector; if not, short out the whole machine with Control Electricity (Forces 3 - also Covert). The latter solution is likely to lead to a pat-down search, though, and that's inconvenient if you don't have a backup plan. I would personally allow a mage with Forces higher than 2 to use amped-up versions of Transmission to cover shortcomings in the Science department.
Fate handles this issue sort of similarly to my idea for Life's Honing the Form solution, but instead of improving his Dexterity, the Fate mage improves his chance of success with various Fate manipulations - starting with Exceptional Luck (Fate 2 - Covert, but with an annoying Mana cost) at the low end. Lucky Coin (Fate 3, Covert) is entirely reasonable, Superlative Luck (Fate 3, Vulgar, Mana cost) is sort of excessive, and Probable Cause (Fate 4, Vulgar, Mana cost) is just beating destiny over the head. The nice thing about Lucky Coin is that it stacks with any one of the other three spells I've listed here.
Time follows Fate's lead, unsurprisingly, but at lower Arcana. Perfect Timing (Time 1) is a solid choice for increasing that Dex + Larceny pool, and Glimpsing the Future (Time 2) is the same but better. The stylish solution, though, is to cast Temporal Stutter on your weapon, just before the inspection.
Then there's the really stylish solution that combines Fate, Time, and Matter.
The mage shunts an object forward in time until just the right moment.
Duration: Conditional (p. 150)
The targeted object disappears entirely until the mage performs or experiences the specified condition. It cannot be detected or retrieved by other means; it does not exist at intervening points in time.
Rote Dice: Intelligence + Occult + Time
A variant that uses Space:
Nothing Up My Sleeve (Space 4, Time 2, Fate 2)
The mage hides the object in a dimensional pocket until just the right moment. Not for use on lagomorphs or doves of any kind.
The targeted object returns to hand (or drops to the ground if the caster does not have a free hand or does not wish to catch it) when the mage performs or experiences the specified condition. It could potentially be retrieved by other means, through the use of Space magic.