It's right-hand fingering shorthand, used more often in the 1800s and early 1900s.
. - I, .. - M, :. - A, + - P
P = Pulgar/Thumb
I = Indice/Index
M = Medio/Middle
A = Anular/Ring
E = Mignolo/4th (pinky)
This is probably an obsolete notation for right-hand fingering, instead of the modern p,i,m,a,e notation.
I guess that + means pluck with the thumb, and 1-4 dots mean use the corresponding finger.
A similar (but not identical) notation was used by Mertz in a 19th-century guitar tutor, see https://imslp.org/wiki/Special:ImagefromIndex/442101/torat page 10.