Abbreviations are always a subject of discussion, how should they appear, here is some helpful advice.
To follow strict rules of abbreviations, unless the abbreviation is in capitals, a full point should always follow.
The approved abbreviations for the days of the week and months would appear like this
Sun. Mon. Tue. Wed. Thur. Fri. Sat.
JAN FEB MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC
If it is a mixture of upper and lower case it can have a mixture, for example I.o.W (Isle of Wight), Ltd. (Limited), St. (Street), Ph.D., exceptions would be Dr (Doctor), Revd (Reverend), Mr, Mrs, where full points are not required.
Use a full stop for a footnote, i.e., e.g., c., p., pp., a.m. and p.m., all in lower case.
Use St for Saint, C (for centigrade) and F (for fahrenheit), also without a full stop.
As a rule print century in full, as in nineteenth century, and not 19th cent., with 8 per cent and not 8%.
These are British rules, as taken from Hart’s Rules for Compositors and Readers, as published by The University Press, Oxford (1982).
There will always be exceptions and the important thing is that they are consistent throughout the published work.