Can't help with that, I'm afraid. Presumably it's not altogether legible. If it could be J McWilliam, that could be John, who founded McWilliam sails. The sail would probably need to be very old...over 40 years.
I tried to upload a pic of the badge on here, but kept failing, so I've put the pic on "yacht advice" on Facebook, if any of you visit that page. The maker was based in satchell lane, Hamble.
I worked there for a short period in about 1988. Was Williams, older lady with red hair owned the company I think, manager was a Scottish fellow, Andrew Smith I think, he and I didn't get on. I left not giving much notice, about 3 minutes I think!
It later became Williams and someone, can't recall.
Several oddballs on the staff! One quite scary lady.