Serbia 2010 Year Issue:

SERBIA, PU, really PU, on cover:
If I like something, it is when sender is just perfect Philatelist, care about affixing postage stamp on cover in proper way, than, in post office, insisting on properly applying hand cancel!
PERFECT!

Here we have issue from Serbia, with very attractive topic of "AirPlane", which can be included also in "Aircraft" and probably in WWII too.

Year 2010, with Michel catalog number MH 2, in Scott catalog it is number 527, actually it is issued in booklet format, where sheet of 4 are just put inside cover of booklet, but not affixed to cover itself.

Catalog value for used, CTO or PU, in both catalogs, are almost same, around 7.50 US$, normally, on cover have it little bit more, and with properly applied hand cancel it will be with premium market value, for sure, if You will find someone willing to sell it, because booklet was printed in just twenty thousand samples!

Good luck in finding it on market in properly used condition!

The AR label is for "Avis de Reception" (Notice of Receipt)?

"...The AR label is for "Avis de Reception" (Notice of Receipt)?..."

Correct!