I'm not sure if this is a bug, but I didn't think luminous signpost was a "helpable" culture when visiting neighbors? Even if that is the only culture available, I don't want to hit that, as it offers so little culture.. Thanks
Indeed, those hands belong to the, in your case, invisible flying boat. So, this is not a bug.
Invisibility can be caused by many factors, like slow internet connection, browser, its version, flash player's version and so on. I'm not an expert for computers but if you have problems with invisible buildings all the time, please contact support. I'm used on 'invisible' buildings due to slow internet connection i have .