While walking past an old (W-reg) landrover in Llandaff North today I noticed a few moss tufts growing from joins in the bodywork. There was no-one around so I grabbed a few tufts and stuck them in an empty crisp bag in my pocket. Checking the specimens when I got home revealed four species: three Bryum (no prizes for guessing which: capillare, argenteum and dichotomum) and Ceratodon purpureus.
I'm never quite sure how to record plant species which are literally mobile - I guess the car probably spends most of its time outside its owners house, which would be the best place to pin the records to, but without knowing this the best one can do is record the location where the species were seen. Sam, I note that you mention two species recorded growing on your car in your Pembs flora, but didn't add records of them for all the county tetrads though the mosses would have visited them all :-)