In the fall of 2013 I started building my small web-site with programming problems - CodeAbbey. Soon it become obvious that most users fall off after solving from 5 to 20 tasks - but few are very persistent, doing over 100 and sometimes reaching the top.
So I started awarding free Certificates for solving certain amount of tasks (now 145 - read more). They have unique numbers so they could be checked at user's profile page - or added to LinkedIn by link. Depending on skill some people reach this in a month while others in a year or two...
It appears, people like them - even so that some tried to cheat :) Though it is annoying to verify pretenders' solutions manually, I'm on the other hand usually feel very pleased by such devotion.
I don't mean you need immediately join us :) As these certificates are just funny things and not recognized officially by any University or Company, of course. I just have come to boast a bit, since I'm somewhat proud of this idea of motivating people anyway!
Here is example of certificate for some outstanding colleague: