aloha cathie -
i was just reading somewhere about a gel you can buy to make your socks "slipper socks" (you squeeze it on and it makes non-skid socks). i can't for the life of me find the actual product but found blogs online that some people use liquid latex rubber or puffy paint another link for puffy paint. i'll keep looking for it though.
i think i found it! Here is the link and you can use a stencil to create what you want on the bottom. If you do a search for Regia ABS Latex you can find a places that sell it in different colors. Yay!