OB Poem

As poet George Dance describes and explains it, the 'OB Poem' form is, basically:

"Someone posts a poem you enjoy reading; you post one back to them. The latter is an OB poem. I don't know for sure, because it's a tradition that long preceded my arrival on Usenet (where I learned about it), but: I think it comes from OBligation; as in Eric Frank Russell's sf story 'And then there were none...', where the society had no money but traded ob's instead: If someone did something for you, you'd be under an ob, and have to clear it. Similarly, if someone's poem affects you, you clear the OB by posting one of your own for them."

How would the average contributor know that the poem was meant to be an OB poem?

"They probably wouldn't... as it's a tradition from another place Usenet; but then they wouldn't have to. I wasn't saying it was in bad taste for you or anyone else to critique it; I'm only saying it would've been in bad taste for the poet the OB poem was written to unless explicitly invited to."