However, the most common and widely understood way to indicate an enclosure is to simply write "Enclosure" or "Enclosed" followed by the number of items enclosed, like this:
* Enclosure: 1
* Enclosed: 2
Alternatively, you could use "Enc." for a more concise abbreviation, but be aware that it might not be as widely understood as the full word.
Important note: It's crucial to be consistent with the abbreviation you choose throughout the letter.