what are the marks's meaning?

I always see the marks on the upleft corner of the TV screen, like "TVPG"  "TVPGV" "TV14LSV"....
what do they mean???

These are "Ratings" put up for "parental guidance."  PG=parental guidance: i.e. children show watch this at the permission of the parents or only with a parent.  LSV(L=coarse language(swearing , profanity, 4 letter words), S=S_ex: explicit s_ex scences, and v=violence. 14, 18 are ages. PG18=parental guidance or only for people over 18 (depending on the region. In some states 18 is the legal age).  Personally, I think the censors have gone over board since sometimes documentaries depicting war scence has the warning "the following contains scences of violent..."

  When a person turns 18 or 21 (depending on the country, state or province) he/she has certain legal rights, one of which is the right to privacy.  Teachers cannot inform other people, including the parents, of the mark this student has unless he/she has consent the release of the information.  Teachers should not post marks on their doors with names on it (only student numbers.) Actually, legal or not, it is best not to unduely embarrass a student by putting up his/her name.

專業，謝謝