How I quickly and easily tell MS from PL.
Earlier coins (Pre-1954) that were specially struck where called Proofs. These specially struck coins presented crisp legends and sharp details using fresh dies, likely struck slower.
By about 1949, coins were being produced with such quality that they resembled these specially struck coins, and the designation Proof-Like was "coined".
Those earlier Proofs, we now called Specimens. All early coins guides called them Proofs. The designation Proof-Like started in 1954 or shortly after..
The mint made Specimens (Proofs) in early years and consistently from 44 to 1953 and stopped. They made Proof-Like sets starting in 1954.
So from 1949 to 1953, we have Proofs (specially struck, now called Specimens) and we also have coins produced that were called Proof-Like.
A lot of people look at the mirror finish in the fields of the coin, but that's not exactly a good method. Many coins have toning, so you can't used that. The best way I have found, which makes the most sense to me, is the finish on the legends. Proofs, Proof-Like and Specimens "always" have crisp, frosted or pristine and sharp surfaces on the legends. Very rarely do MS coins produced this level of strike. Generally I have found some MS coins that contain sharp and frosted sometimes, but not the same at all, and quickly you can find legends somewhere else on the coin that are beaten up, rounded off etc..
SO look at any PL or early SP coins and this what you will see, regardless of toning.
Telling the difference from 1953 SP to 1953 PL is another matter..