Position will always be determined by the root note of the scale. The scale diagrams on this website show the root notes as a black dot or an ‘R’.
The pentatonic first position for instance can be a good indicator, your index finger is on the root note for a minor and your pinky is on the root note for major, so for example you’re in the a pentatonic shape, fifth fret, start on that note (A) for a minor solo, or the pinky (8th fret) for a c major solo, just emphasise the root note, minor or major.