Ron Guth:
Several varieties of the 1793 Chain Cent exist. The "Periods" variety has distinct periods after LIBERTY and the date. Since neither of these were abbreviations, the presence of the periods is puzzling.
This is the scarcest major variety of the 1793 Chain Cents. As of July 2011, PCGS had certified only 70 examples, with only one (a single PCGS MS65BN) in Mint State. Reflective of that fact, no Red-Brown or Red examples are known.
The 1793 Periods Chain Cent is under considerable demand from die variety collectors, major variety collectors, type collectors, and first-year-of-issue collectors. The fascinating chain design on the reverse is another attraction.