I have never really understood some people's inability to deal with these. It's as simple as 1, 2, 3. Really.
1. Missing Letters
2. Belonging
3. NOT in Plurals
1. Missing Letters: In the line above It's is short for It is, so the apostrophe replaces the missing i in is. The worst case (as my old English teacher, Mr. Midgley, taught me) is forecastle - the front part of a ship, which, when spoken correctly sounds like 'folks-ll' and should be written
fo' 'c's'le.There are many other examples when conversational words are written: Let's = let us, we'll = we will, should've = should have (NOT should OF !!), two penn'orth = two pennyworth (Mr. Midgley said that where two or more should be used, it was acceptable to use just one to prevent clutter) and so on.
2. Belonging: Wallace's wrong trousers = the wrong trousers belonging to Wallace, Mum's drawers = (the chest of) drawers belonging to Mum, and so on. Is the apostrophe before the s or after it? It should be placed so that the whole word before the apostrophe tells the reader to whom the object belongs. But watch out for the one exception: 'its' has NO apostrophe (ever!) UNLESS it means 'it is'. It's the dog that chased its tail!
3. NOT in plurals: So many examples are wrong because people put an apostrophe in where it is not needed: in plurals. The question to ask is "Is the word I'm using to do with belonging, or does it have missing letters, or is it just more-than-one-of -the-thing-I-am-talking-about? If it's just more-than-one....etc., you don't need an apostrophe.
So to analyse the pics: 1 to 9 inclusive are all wrong because they are plurals.
10 (Tynemouth) presumably is short for 'That is', so should be That's.
11 (Rawtenstall, Lancs.) is a real maverick - wrong because an apostrophe is never found in verbs ('doing' words) such as those shown.
12, a notice in the corridor of a hotel in Southend, is a classic in having a wide selection. Event's, Birthday's and Executive Suite's all wrong (just plurals), Ladies Night should be Ladies' Night (apostrophe after the s because the Night belongs to the Ladies), BUT Mother's and Father's Days are CORRECT!