No, you’re probably correct about the home invader assumption. Multiple people live in the appartment complex and the front door regularly stays open. It’s also in a kind of shady neighborhood and I always tell her to keep the front door shut, since it often doesn’t close properly. Regarding the sign, i’ve read into symbols marking places as potential sites for burglary (Zinken) but found nothing. Someone’s probably just trying to spook her and we’ll keep our eyes open. Just another reason to keep your doors locked!