It appears to be an " anti billowing " rotation stop , for the roller tube , it's function will make more sense if you look closely at the hook as it relates to another hook on the coach body when the awning is retracted.
It designed to stop the tube unrolling the awning fabric, while driving in a cross wind.
Seems like it would also be useful for keeping the awning material located in the tube to keep the arms square to the coach body while retracting .
99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.