Old red tag for address

While doing a recent survey in an unincorporated neighborhood, I noticed that some buildings had regular addresses: “123 ABC Street”, some nearby buildings only had a tag that looks like a long 5-6 digit number on a red plaque, some buildings had both.

I am specularing the tags are either old addresses or Fire Protection District IDs. The newer & incorpotated neighbourhoods a few blocks do not have such tags.

I checked the local GIS and it only mentions the new addresses for the same buildings.

Does anyone know what these tags might be, and how it should be mapped?
For now, I added them as “ref=NUMBER”.

I found one place on the GIS map that uses the long tag number as address.