Obfuscate

The rules for Obfuscate are on pages 184 - 186 and the rules for using Auspex to see through Obfuscate are on page 142.

Remember that, by the book, Unseen Presence does not grant invisibility. It instead warps peoples' perceptions and makes them dismiss you as unimportant. It's all about not drawing attention to yourself: don't make noise, don't open doors, and so on.

With those reminders in place: while you can use Obfuscate to help yourself set up an ambush, drawing a weapon while obfuscated explicitly counts as an attention-drawing action and requires 3 successes on Wits + Stealth vs 7 if you are within anybody's line of sight (not just your target's). Obfuscate does not cover weapons held in your hands (see p. 184 - 186).

If you are within anybody's line of sight, then the act of aiming your weapon or approaching somebody with a weapon WILL shatter the fugue automatically, just as crashing through a window or yelling would.