In spelling systems which use it, the line above the letter פ called rafe indicates that it should be pronounced as a fricative: פֿ = /f/. The diacritic rafe goes together with the diacritic dagesh which indicates plosive pronunciation, in the case of pey dagesh it would be פּ = /p/. Without going too much into details, it must be said that dagesh in pointed Hebrew texts has other functions as well.
The second diacritic, the small dot beneath pey in פִ, is called hiriq and indicates vowel pheneme /i/. If you find פִ in a fully pointed text and the letter pey does not have a dagesh, the whole combination would indicate /fi/.
The above is universal for Hebrew and Yiddish but:
- the diacritic rafe is not used nowadays in Hebrew while in Yiddish it is only used in some spelling systems (see below).
- hiriq is used in pointed Hebrew texts but in Yiddish it is used only in some spelling systems to avoid ambiguity in pronunciation of the letter yud י, so you would not encounter it under letter פ unless it's a Hasidic children's book or some pre-WWII book using now obsolete spelling.
In a supermarket in Israel you can find the following renditions of the Yiddish "gefilte fish" into Hebrew:
- געפילטע פיש - this is really just (unpointed) Yiddish
- גֶעפִילְטֶע פִיש - I don't think I've seen this in reality but this would be the expected pointing to help someone who does not know how to pronounce it (it's used e.g. in Hebrew Wikipedia).
In modern Yiddish texts you would find the following variants:
- געפילטע פיש - this would be the spelling among the native (mostly religious) Yiddish speakers nowadays and the prevailing spelling in books published around mid-20th century and later (but unfortunately less so nowadays).
- געפֿילטע פֿיש - this would be the spelling according to the Soviet and the YIVO orthographic systems. The YIVO system gained popularity in academic circles with the decline of Yiddish among secular Jews.