This is used in a fame level 1 Grauberg_A repeatable "Chocobo Panic" started at Kuoh Rhel (G-7). According to wiki it can reward WHM and DRK hand seals.
These appear on AH under the "Weapons > Ammo & Misc. > Pet Items" category even though they're for a quest.
To elaborate on the other comments, these are indeed used in the Chocobo Panic quest. This quest will net you 400 Cruor the first time it's completed and 200 every other time you repeat it plus a chance at one of WHM, DRK, THF and BRD hand seals. I did this quest for THF seals.
To give you an idea of the seal droprate, I bought 8 stacks of these greens and had two left over. I landed 8-10 of each seal before finally landing the 8th THF seal.
This quest can also net you the Indigo Abyssite of Confluence by trading 10 Woozyshrooms to the chocobo one by one. This Abyssite reduces the cost of Conflux travel.
