Some of the cell tower lease buyout companies (see http://celltowerleasebuyout.com/
) do data mining for leads - using property records to try to find property owners with cell tower leases to purchase. These companies don't check the data that closely- cheaper to send the postcard/letter than to confirm whether a tower is actually there.
Each cell tower lease buyout company is different- so the reference number likely refers to their internal site number they assigned to this "lead". Other than calling them back- I don't know how you would find more information.
Hope this helps.