I kind of consider salary numbers posted in job ads to be a bit of a red flag. In my experience, when that happens, the company's usually trying to preclude negotiation on a salary that is way below market rate -- and there's amost always room for negotiation, so I see companies that try to do this as probably kind of sketchy (except in the case of some government jobs where they may be required by law to post salaries, and there really is no room for negotiation as their salaries are also set in stone).

The other situation that I've seen this in is job ads posted by recruiters who post way-above market-rate salaries and then try to bait-and-switch you when you answer the ad. Also a big red flag.

Mostly, though, I am interested in negotiating, and don't want to commit to a number even before I've had a chance to make a favorable impression on the employer, because then they could say "well, you knew ahead of time what we were paying, so why are you trying to negotiate?" Well, if they had posted a realistic number or their best possible offer, maybe there'd be no need to negotiate -- but that is virtually never the case.