Well, I don't know how unusual this is, but I like to take pictures of animal crossing signs, because different countries have different animals that are crossing.
For instance, in Namibia, I took pictures of warthog crossing signs and elephant crossing signs. (Of course, I took pictures of warthogs and elephants, too.) On Isla Santa Cruz, in the Galapagos Islands, I took pictures of tortoise crossing signs. In Costa Rica, I took pictures of crocodile crossing signs.
And, I guess I take pictures of other "different" or new-to-me signs, also, such as the trombone with a line through it in Vietnam (no honking). And, this isn't a sign exactly, but the pedestrian crossing lights in the old part of Mainz show little dwarves (I think) instead of the standard people icons.
I also take pictures of doors. In Europe, in particular, there are so many beautiful old doors and unusual door knobs and knockers. However, I know quite a few people who do this.