I would suggest sticking with normal url path structure, like /x/path

Why break the convention? For what purpose?

$ is something I associate almost exclusively to being for symbols of equities and currencies. e.g., $AAPL, $BTC, $USD. (or, for amounts, $100 would indicate 100 unites of USD, or whatever the local currency is in countries that use "dollar" (e.g., Canada, Australia, Hong Kong, etc.)

Before @ was also for usernames, it was mostly used in e-mail to separate username from domain namespace.
But as Twitter used @ for username, that's now common across social media, e.g,. how @cointastical, is accommodated here on SN for nym (username).

On Fediverse, @ is not only used for username, but also for separating the username (or whatever) from the domain namespace. e.g. , @cointastical@bitcoinhackers.org

On Lemmy (a type of Reddit for the Fediverse), they use "!" to "tag" a "community".

So with Lemmy, !bitcoin@lemmy.ml is a tag for lemmy.ml/c/bitcoin community, where "community" is a namespace equivalent of how there is a "subreddit" with Reddit (e.g., r/Bitcoin). If I am referring to a community within my current instance, I could use !bitcoin without the domain (@lemmy.ml) part of it.

Coincidentally, lemmy.ml just did something to their site where the normal site is responding the same as join-lemmy.org, ... just recently, not sure what's going on with that. So, use another instance to see this:
https://lemmy.cat
which shows an example of a community
https://lemmy.cat/c/coronavirus

But see how they are still using c/ as the URL routing to indicate community?

So in a comment if I reference that, I would write something like
"Check out the pinned post In !coronavirus@lemmy.cat, it will be useful!"

But for a URL, I would write https://lemmy.cat/c/coronavirus

Blame Reddit or whatever, but maybe that x/sub scheme should be consistent here in Stacker.news

stacker.news/s/sub for the URL, but in a message I would write
"Check out @k00b's post in !somesub".

For the clickable URL for that, SN would automatically make that "https://stacker.news/s/somesub" ).

The reason for this ... let's say I were to make my own instance of stacker.news from the github repo, say for my (hypothetical) Japanese anime project (myanime.jp), I could reference in a comment !somesub@stacker.news and the URL would then be automatically generated https://stacker.news/s/somesub ).

So that's my suggestion:

• Something like s/sub for the URL's path.
• !sub to mention a sub in a comment (and becomes a link to the sub without the user having to provide the URL).
• And for future compatibility when SN software is used by more than just one domain, accommodate !sub@domain.com