I use a broad triangular pencil marking at each edge of the front of the fingerboard to correspond where the single dots would customarily fall on a bass guitar, and a rectangular pencil marking where the double dots would be, up to the octave position. I know they aren't precise; they are just rough guides to give my extremely visual brain a sense of portioning and overall proportion. And if note positions are different because of temperature fluctuation, visual angle, imprecise pencilling, etc., my brain picks up on that very quickly and makes adjustments.
And even though they have frets, I would be lost without any dots on my guitars; in fact, I have a much easier time with dots like on Brian May's guitar (• 3rd fret, • 5th, • • 7th, • 9th, and • • • 12th, for both octaves), and I wish all my other guitars (bass and standard) had that pattern. Invalid Link Removed
It's just how my brain is wired for almost everything I do, always looking for or imagining visual reference points and landmarks, seeing/imagining shapes, zones, contours, for eveything (even for non-visual/abstract concepts). While I think actual guitar-style dots would look tacky on a double bass, other forms of markings don't bother me so much. And pencil graphite doesn't really stand out very much at a casual glance.