The two other stamps belong to a set of four issued on the 5th of September. This set is the second in a series started last year about extreme sports. In 2006 the set of stamps was about skateboarding, this year it is about inline skating. The stamps picture a Flip and a Drop-in, two figures of the inline skating. This sport is more and more popular in almost all countries, including South Korea, where professional inline skaters start to appear.
You may notice something else on the cover : the small red bars that are located at the bottom of the cover are crossed. These bars are printed by the machine that are doing automatic sorting of the mail. It seems that during the automatic sorting of this cover, there was a error, the cover ended in Sceaux, another city of my department, but not in Montrouge, the city where I live. The cover was sent back from Sceaux to Montrouge by the postal clerks (There is a cancel from Sceaux on the back on the cover). Prior to that they had to cross the red bars to make sure the machine would not route again the cover to the wrong place ! Such mistake happens from time to time.