Even the most veteran motorcycle rider out there, will not known every road sign. Many road signs are added over time, so at times you see one that makes you want to scratch your head and go 'hmmmmm'.
AutoInsurance.org have produced a do-it-yourself quiz on the internet. They show you 20 more or less unfamiliar road signs, and you get a multiple choice to answer. So pretty nice to see if you really know the road signs.
I did it, and believe it or not, I passed! 20/20! A+