Yes, its a good luck flag.
The writing is all good luck phrases and names. The largish characters on the far right say 祈武運長久 (Good luck in battle). The words under that bit may well be the recipient's name, but its a bit hard to make out. Maybe TAKAFUJI ?Marō 高藤囗マ郎. Can't read the middle character. It's a bit unusual to see the name without an honorific attached to it, but not entirely unheard of.
A lot of people who signed the flag have the surname of HASEGAWA, so I'm guessing this flag was presented by a neighborhood association, rather than a school or workplace. Most people have signed with some sort of generic good luck phrase next to their name ("good luck in battle" is repeated several times on the flag).
There is a poem written under the large words on the right. Something about a cherry blossom blossoming, which is a typical image associated with warriors going off to battle. If you've seen the movie "Last Samurai" then you know what I am talking about.
