HaegerAshtrays.com
No. R-1820-S
Nesting Ashtray 6¾" circa 1958, Ebony Cascade glaze, photos courtesy thebrassmonkeyatpeytonsplace on eBay
Note: The above information is for R-1820 as R-1820-S has not been found in a catalog and they are assumed to be the same design. An example marked R-1820 is not known.
Bottom reads: ROYAL HAEGER R1820-S U.S.A.