When free app Foursquare announced an injection of $41 million from investors earlier this year, CEO and founder Dennis Crowley described how the new funds would help the mobile search and location-sharing platform move away from its perception as a simple “check-in app” and “get closer to being able to prove that there’s a real business here.” A lot of that proof has been coming in the form of advertising on the service, and on Monday the company is unveiling the latest development on that front: Foursquare Ads is now being opened up to advertisers of all sizes, targeting Foursquare’s 40 million users worldwide. Will it be enough to help Foursquare become the mayor of local mobile ads? Monday’s news is an encouraging sign of progress. It comes after Foursquare first opened the platform to a limited number of large advertisers — some 50 in all — about nine months ago.