I always make a label. I used to mark with a pigma pen, but found that those tended to fade after multiple washings, plus my handwriting isn't perfect. So, now, I print my labels on fabric with my ink jet printer. I iron freezer paper to the back of the fabric to stabilize it, then run through the printer. Make sure there aren't any loose threads. Here's an article on how to do it:
http://www.art-e-zine.co.uk/imagefabric.html . I have also taped down the freezer paper/fabric to a piece of paper and ran that through (when the piece of fabric was too small). I usually print the label on a piece of copy paper to gauge the placement before I run the fabric through the printer. Afterwards, you just iron the label to set the ink.