As a flow-on from the Milan design fair, Ikea set loose a team of street artists in Milan to stick B&W stenciled figures on subway ads (it had already bought), turnstiles, steps etc. It was all with agreement from the metro system and, one presumes, payment to them too.
Not sure this really fits Ikea and its not really guerrilla marketing but its a tame corporate version thereof which just might work for a marketer who wants to appear rebellious even fi they’re not.