Some tags currently have it, and some do not:
Let's standardize this. Additionally, we should decide whether or not to include the "A1" (which means that this is a patent's first filing) at the end of the patent number.
This site is interested in both issued patents and patent applications. The designations for them differ.
For a patent application, use the prepended year as shown on the PTO website http://appft.uspto.gov/netahtml/PTO/srchnum.html :
Example: Utility : 20010000044
For an issued patent the options vary, but the form we are most interested in is a 7-digit number as shown at http://patft.uspto.gov/netahtml/PTO/srchnum.htm :
All patent numbers must be seven characters in length, excluding commas, which are optional. Examples: Utility -- 5,146,634 6923014 0000001
The tags we use should follow these patterns. They could perhaps become links to PTO source materials.