Which (if any) is correct: est., estd., or est'd.?
Solution 1:
There is no single correct way to write it. Estd seems more common on older signs, or things that were established longer ago.
I've seen Estd written in many different ways:
ESTḌ 1862
ESTD 1824
ESTD 1817
Estd. 2001
Likewise for Est:
EST. 1946
Est. 2002
EST 1937
The capitalisation usually depends if the accompanying name or text is capitalised.
Solution 2:
Heinz factories buildings (some are no longer producing) that are now Apartment Lofts in Pittsburgh has the abbreviation for Established as EST'B'D.