To focus specifically on emojis rather than fonts, while using them in a title purely as illustration might appear spammy in most cases, I think there is one situation where this actually adds value...
Permit relevant use of emojis in the title when the emoji tag is required for the puzzle
Here's an example of what I would consider a decent emoji puzzle:
🍩🔔🔥Scrambled emoji tale⚛️🎶🛒 #2️⃣
In this instance the puzzle involves interpreting the emojis within the question body to identify something from popular culture (I won't spoil it for you here). While the title could have been written without any emojis at all, picking out a few key ones here and inserting them in the title as an extra hint to the solution is a great twist on the very common (and widely praised) device of hiding a hint in a puzzle's title.
On PSE we usually applaud a clever clue concealed in the title when done with words, and the use of good visuals in a puzzle is also something which is rewarded with many upvotes - it's clearly something the PSE community values. Combining these two, if there existed a way to include visual clues in a title it follows that this might also be considered a clever piece of puzzle-play by the creator. For this reason, I do not think we should blanket-ban the use of emojis in a title.
HOWEVER... I think that the reason the emoji usage in this particular puzzle's title come across as very clever is that this is an emoji tagged puzzle. The use of emojis in this title is entirely in keeping with the theme. If emojis had been used, say, in the title of an affix-riddle puzzle with absolutely no relationship to emojis, I would consider that spam or clickbait-type behaviour. Likewise, if an emoji puzzle just included a random or irrelevant selection of emojis in the title 'for the sake of it', what does this actually add to the puzzle experience? The emoji tag is already there; we don't need another reminder!
So I think there's a contextual element at play. In my opinion a good rule of thumb would be:
- For an emoji puzzle, relevant use should be allowed.
- For other puzzle types, emoji use in titles should be discouraged.
In all cases, I think it would be best (and polite) to engage with the user who has used emojis in their title to discuss these points before simply editing them out - at least for the first time they do it. In my experience, explaining an edit action which isn't just an obvious retag or spelling/grammar correction usually generates better feeling than going ahead and doing it without any conversation.