That would be a 'seam ripper', Winter Wolf.
Works well, but you have to be very careful not to rip threads from the actual fabric as opposed to the ones holding the patch on or creating the logo. I tried to get a logo off a very nice polo shirt my husband got as a prize at work once. Had great luck despite the black thread on black fabric being hard to see. Then about halfway through I snagged a thread from the shirt and that was all over. It unraveled and made a fair sized hole...had to toss the shirt as it was impossible to fix that neatly.
[ 11-09-2006, 09:06 AM: Message edited by: Cloudbringer ]