The MLA Handbook for Writers of Research Papers : "Do not use an apostrophe to form the plural of an abbreviation or a number" and the examples include acronyms such as PhDs and VCRs. The Chicago Manual of Style : "So far as it can

I know apostrophes don't normally indicate plural, however someone said that if used in abbreviations it is acceptable: gig's (gigabytes), mp3's, DB's (Data bases), PC's, etc. Is this true? When I was a pre-teen, I was taught