It's fairly durable stuff - it's made to be UV resistant and to take abuse from the road _ rain, ice/snow, dirt etc. It's not forever though - the color can be worn off and it will fade eventually. I would think it would be a two to five year deal depending on conditions- YMMV.
I work on some of the hardware that can print this stuff so I have a fair amount on knowledge on the production side of this and good knowledge of application.