I have seen titles, such as books or business names, that omit the apostrophe. Is this proper? Can a title be apostrophe free if the author chooses? EX: Tom and Sallies Big Adventure. Should Sallies properly be Sallie's? Or Sallies'?
Apostrophes should be used in titles as in body text. To omit an apostrophe can change the meaning of the words.
There may have been some historical scenarios in which they’ve been omitted for technical reasons (e.g. apostrophes in filenames used to cause issues, though I can’t think of any good reason why they’d be omitted in printed headings or titles.
I've read, somewhere in the dim and distant past, that it is accepted practice to disregard the apostrophe for headings, subheadings and names of events which are capitalised. e.g. I recently received a missive from my child's school, which included the title: Parent's Evening (implying that the evening was for the sole use of 1 parent) Parents' Evening would be more correct, but omitting the apostrophe (for the title/heading) i.e. Parents Evening - is acceptable. Obviously, an apostrophe is needed if it's used in the body of a text e.g. Next week's parents' evening will be held online.