I have been using PLA filament for two years now and have had good prints. ABS on the other hand has not been so good, so my choice of filament is PLA.
I am getting ready to do a sign for the American Legion and the colors are black, blue, and red and are 0.8 mm thin. The black letters are 4" x 2.5", blue are 3" x 2" and the red are 7.75" x 5.5". I plan to treat them with UV protection spray and attach them with clear epoxy to white back lit Plexiglass.
As the letters are quite thin, my question is how well will this hold up in the weather? The sign hangs on a pole that points east & west so the letters will be facing north and south. The original was painted with spray paint and the red paint south side faded to the point you could hardly see it at all. The sign had been there for some time and was done at a professional sign company.
I printed a handle for a rather big rolling door in natural PLA (From Fabberparts) - no UV protection. It's on the weather side of the house and is exposed to direct sun half the day.
And after three years cycling to all the German seasons it's still absolutely fine. Also, Wikipedia told me that PLA has good UV resistance - so you should be fine IMHO.
Here is a good blog post about your question: Using PLA for Long-Term Outdoor Applications.