I've thought about it in the past, but I haven't the slightest idea how it would be done. I'm a decent ASL signer, and my wife is fluent (she has a masters degree from Gallaudet University in Special Education of Multiply Handicapped/Hearing Impaired), and we have lots of deaf friends. But it seems to me that any sign language grammar has to be spatially oriented, and really wouldn't be related to lojban any more than ASL is to English (i.e., not at all), nor would it be advantageous to do so.
--gejyspa