The main symbols to be identified for plastic recycling are

Polyethylene terephthalate is indicated by the abbreviation PET or number 1.
Polyethylene. High density is indicated by the abbreviations HDPE, PE-HD, low density with LDPE, PE-LD. The recycling symbol may contain the number 2 (or 02) for high density polyethylene or the number 4 (or 04) for low density polyethylene.
Polyvinyl chloride is indicated by the number 3 or 03 in the recycling symbol.
It is the symbol of Polypropylene. It may be marked with the number 5 or 05.
This is the municipality of Polystyrene. Reported under number 6 or 06.
Symbol O or 7 (07) may indicate, in a generic way, other recyclable plastics. This symbol can be found on plastics such as Glass Fiber, Nylon, Polylactic Acid, Polymethyl methacrylate and polycarbonate.