Is there any way you can test the signatures to find out if they are colorfast? I would be afraid to wash it unless I were absolutely sure whatever was used for the signatures is permanent. Or, are those embroidered signatures? If embroidered, again you have to make sure that the dye in the floss won't run.
I would hate to send a quilt like this to the dry cleaners; I normally would use either the top-loader method of washing (stop before agitation cycle and hand agitate, then spin out, add rinse water, hand agitate again, then spin out) or a gentle cycle in a front-loader. It is the signatures that give me pause....