Is there an official standard vegan packaging symbol designating that a product is vegan? I'm trying to eat vegan and having a hard time determining (by the packaging) which products are appropriate for me.

Are there symbols or certifications I can look for, preferably something backed by a federal or state government?

If there isn't such a thing in widespread use, then what is the reason for its non-existence or lack of general adoption?
There are two common symbols; the European Vegetarian Union (EVU) and Vegan Action. 




In my experience, you will see the EVU on packaging and on restaurant menus. I've only ever seen the Vegan Action symbol on packaged products.

The EVU is not exclusively vegan so you'll still need to read the packaging or ask about ingredients if in a restaurant. The Vegan Action symbol is exclusively vegan and is becoming very popular in the United States.