$50 Pe

This looks like an authentication marking that some handlers of large amounts of paper currency from other countries stamp on currency after they have deemed it authentic. US $50 and $100 bills that have circulated in other countries show these markings frequently. I believe this is practiced mostly in the Middle East. They come in a seemingly infinite number of designs, sometimes in Arabic script.

Interestingly, I used to work as a bank teller, and Middle Eastern gas station owners would bring stacks of US $50 and $100 bills in with these markings on them. However, the same customers refused to accept ANY $50 and $100 bills with these markings when cashing checks or withdrawing money.

Here's an authentication marking on a US $50 bill: