if placing a guide on your machine bed is not an option- or a pain due to having to remove it all the time why not just draw it on with a sharpie? or nail polish- something that will last, not rub off on your fabric- and not have to be removed? since each machine is different it is hard to say there is a specific tool to use- each person has their own 'need'. one of my machines I used an index card- lined up with the needle- then drew a straight line with a fine tip sharpie- then when it had time to dry I coated the line with clear nail polish- the line has lasted a few years now. I too was tired of having to remove my guide every time I needed to change the bobbin. after years of practice/use I have found my 1/4" and just know exactly where to line up- regardless of which foot i'm using- but that one little old machine still has it's mark on it- when one of the kids are over wanting to sew they like to use that one.
