The signs are triggering the laser detection, I get that all the time with my V1. It's because the light output from the signs has some infrared content in the same wavelength as used by PD laser. Same thing for neon lights, and you'll find other things that do this as well (such as the third brake lights on newer GM SUVs).
Your guess about the radar false alerts is accurate, they are caused by radar-operated motion sensors for doors and alarms.
If you keep your V1 in full-logic mode it will minmize the false radar alerts but won't eliminate them completely.