One more question: Do all English abbreviations end with a dot? There are some exceptions in Polish.
You are getting into fine stylistic territory. Some abbreviations have lost the sense of be an abbreviation. Some loan words which are abbreviations are not understood as such in English.
Units of measure for example are rarely noted in their abbreviated form with a period.
And technically acronyms and initialisms can be considered abbreviations, so there is that large class of with do not use periods. Sometimes folks use periods with some acronyms and initialisms and sometimes not.
Names of our States when abbreviated do not usually take periods.
Academic titles can go either way.
If you find yourself, really trying to get "academic / editorial" English stylistics down, you would do well to pick up a copy of the
Chicago Manual of Style.
There other exceptions, just pointing out some. But usually a period is appropriate or in uncommonly used, not technically incorrect.
