Change:
// @matches issue_32374/index.html '//*[@class="docblock-short"]/text()' 'Docs' // @has issue_32374/struct.T.html '//*[@class="stab deprecated"]'  <del> //      'Deprecated since 1.0.0: text' </del> <ins> //      '👎 Deprecated since 1.0.0: text' </ins> // @has - '<code>test</code>&nbsp;<a href="http://issue_url/32374">#32374</a>' // @matches issue_32374/struct.T.html '//*[@class="stab unstable"]'  //      '🔬 This is a nightly-only experimental API. (tests#32374)$'

Discussion:
Nightly only items have emoji: ! I think deprecated items should have emoji too. For example this item: suggests using coffin emoji in I suggest using fire emoji: :fire:
cc
Hello, I personally think that the coffin emoji convey better the idea that the item should not be used anymore (it's dead). Fire can have multiple significations in my opinion.
For reference, MDN uses (trash can) for Obsoleted and won't work (warning sign) for Non-standard (thumbs down) for Deprecated but still works (*actually, a beaker) for Experimental (that said, I think it's fine to use no emoji)
I commented on the open PR already, but I'll add my sentiments here, too. Other options to consider: I'm personally partial to ~and ~. I think they convey the message of "hey, pay attention, this will go away at some point" without being too strong or prescriptive. I like too given the definition of "deprecate" ("express disapproval of"), and that MDN already uses it. I also like but it may have too much of a "under construction, stabilizing" connotation than we would like, though. I dislike the coffin because it is difficult to tell what it is from a glance (also, it's too grim for my tastes).
and looks more like they mean "unsafe" to me. I like , as it both has a fairly unambiguous meaning and seems kinda cute. is another option but feels ambiguous and is generally inferior to . (on some platforms it looks like it is waving)
I like :coffin: (conveys dead) and :-1: (conveys not recommended) symbol. I cannot understand why :fire: (conveys burning? power?) and :spider_web: (conveys slow?) means deprecated.
It just come to my mind after your suggestion of :coffin: . I think :fire: means things to be burnt to ashes.
already used to mean "unsafe".
Yes, I noticed :warning: already being used. We also use that here.
I agree that conveys "not recommended", but I don't see that as a problem.

"Deprecated" is often synonymous with "not recommended" (especially when compatibility forbids ever removing the item), and that's certainly the most important part of what "deprecated" means for the end user. Without any other context, looks to me more like a snowflake than a cobweb (at least the ways github/gmail render it in Chrome), which obviously doesn't quite work. does look like a coffin to me, but in a way I suspect is fragile. I could easily imagine a slightly different size or image choice making it look more like a cigar or a chocolate bar or something else that obviously doesn't work. A lot of the other suggestions like and and feel closer to "deleted" or "disabled" than the "deprecated" we're after here. I think is one of the better choices for unsafe because it expresses danger without implying that there's any construction or destruction or other temporary work in progress; just a general "be aware" without any other baggage. It also doesn't express disapproval (after all, there's nothing wrong with using unsafe when appropriate). So even if it wasn't already being used for that, I'd keep it there. In the end seems like the strongest candidate for "deprecated", given all of those extremely subjective opinions.
Ok, then I'll add the :-1: emoji for deprecated items!