Hey, some great ideas, folks!
Some of these might work really well for some cases, and I'm sorry I didn't specifically clarify what I was looking for. I want the wizard to be able to summon forth her staff from wherever it is, whether it's lost, stolen, or sitting in its case at home. It would be nice but not essential if she could send it back home, or if she could summon it from another dimension/world (I'd be somewhat OK if she had to look for it in that case, but the campaign involves lots of relatively easy traveling to other worlds).
As for Cosmic, I've seen both here and in the
GURPS Social Engineering playtest that's there's various house rules for this, which is fine--GURPS is about doing it as you want. But in our game, we're going by the book: p. B33 says Cosmic is "abilities that emanate from the universe itself or otherwise defy explanation. This is reserved for gods, powerful spirits, supers, etc." My wizard is just a "normal" wizard, so in our game Cosmic wouldn't apply to her.
I'm thinking it being a Named Possession, which if you don't know is a Perk where your item gains character points as you do as long as you've done something of "spiritual significance." You can trade each character point for 25 points of enchantment if you want (although the enchantment doesn't have to be classified as magical). This would make it hard to figure as Signature Gear, plus every time her staff gains points she'd have to spend her own character points for the increased value, which would be overly expensive.
As an example of how expensive Signature Gear can get when combined with Named Possession, in a TL 3 campaign like hers the average starting wealth is $1000. If she spends 10 of the staff's character points on enchantments, that's paid for by Named Possession. But if it's also Signature Gear, that's 10 * 25 = 250, so the cost is $33 * 250 = $8250 which rounds up to having to spend 5 of her own character points! However, I suppose I could use the Signature Gear option of Ally, Enhancements Constantly and Summonable. I'll give it some thought.
By the way, if you don't have
GURPS Power-Ups 2: Perks I'd suggest buying it. Personally I think it would be well worth it at twice the cost.