When drafting email subject lines, should we use sentence case or title case? And if we use sentence case, would we punctuate at the end of the sentence?

The following appeared recently:

Which is grammatically correct: hard-hat tours or hard hat tours?

Hard-hat tours. Otherwise, it could be misunderstood as a difficult tour of a hat.

The following, however, is from the entry on hyphens:

two-word terms, particularly those used as nouns, have evolved to be commonly recognized as, in effect, one word. No hyphen is needed when such terms are used as modifiers if the meaning is clear and unambiguous without the hyphen. Examples include third grade teacher, chocolate chip cookie, special effects embellishment, climate change report, public land management, real estate transaction, emergency room visit, cat food bowl, parking lot entrance, national security briefing, computer software maker.

Is your judgement genuinely that the phrase hard hat tour risks – in all seriousness – being misunderstood as a difficult tour of a hat? How does it differ in clarity from emergency room visit? One is far more likely to visit a room as a matter of urgency than to undertake a challenging expedition through an item of headgear, but somehow, emergency room is judged to be obvious where hard hat is sufficiently obscure as to lead the reader into an assumption of something fundamentally ridiculous (and well-nigh impossible).

I would offer that the actual answer to this question is that Merriam Webster lists hard hat with no hyphen and attests its first use as being in the 15th century, which makes it rather more established as a term than the acceptably nonhyphenated climate change, computer software or chocolate chip, and so – although there is no fixed rule on hyphens – the writer can be confident that the reader will not mistake the phrase for indicating a difficult tour of a hat, so no hyphen is required. The opposite to the answer as given, in other words.

I work for an organization that uses commas instead of "for" or "of" in job titles. Managers insist on using these commas even if the title comes after a name: John Smith, director, marketing, will speak at the event. The title is "director, marketing," according to the manager. My inclination is to go with: John Smith, director of marketing, will speak at the event. Is the manger's preference acceptable? Thanks!