Sorry to derail with a serious, on-topic reply ()...
Here’s what Wikipedia has to say (so you know it’s true!):
Marker dots (see Inlay (guitar)) on the face of the fretboard are usually placed at frets 3, 5, 7, 9, 12 (double dot to indicate the octave), 15, 17, 19, 21, 24 (double dot to indicate the second octave). It's also common that there are marker dots on the "upper" side of the neck, near the edge of the fretboard, where the player can easily see which fret he or she is on. Sometimes the dots are replaced with bars, the octave positions having a wider bar. Classical guitars almost never feature position markers, especially on the fretboard's face, whereas electric guitars usually do. This is due to several factors:
1) Electric guitars do not rely on a resonating body chamber to produce sound and therefore the inert bodywood may be carved more deeply to allow better access to higher frets.
2) Electric guitars also sport an extended high-end range, due to the above reason. Typically, up to 24 frets are used.
3) Electric guitars vary greatly in terms of scale length, depth of lower and - if present - upper rout and where these connect to the neck at its heel, and number of frets (usually between 21 and 24). In contrast, classical guitar dimensions are standardised, with the 12th fret aligning with the neck-end of the body, use of only 19 frets, and scale length of 25.6".
While it may be perceived that position markers are featured on popular instruments to accommodate their typically lesser-educated users (in contrast to classical instruments), on the contrary, for the above reasons, position markers are of much help to electric guitarists of any level of competence.
...actually, I did the same thing...