I use blue painter's tape and put the edge along where 1/4" in. I actually also measured other commonly used measurements such as 1/2 and 5/8 and drew them on the tape. I've never had any problem with painter's tape taking the finish off anything or leaving goo of any kind.
As far as the walking foot goes - the outside of the foot is 3/8". Mine has some cut outs on the presser foot and the edge of one of the cutouts is 1/4". I only use my walking foot for quilting layers. For piecing I use a regular foot so it is rare that I need a 1/4" seam when using my walking foot. If I'm quilting with the walking foot I just use the edge of my presser foot (which is 3/8) as a guide or use the longer guide which fits into the back of it if I want a wider distance between rows.