Well, over the last while or so, for me definitely in the last year, I have noticed people on very regular occasions attaching indicators such as /j, or /s, or /q - Its probable that quite a lot of other ppl here have seen this sorta thing as well.
After doing a bit of research, I have found out that tone indicators are actually a really useful way to convey the meaning of your message to someone, as if you were talking in a certain tone IRL - which makes it way easier for people to understand what your message means across the internet, especially for those who find it hard to interpret that kind of thing. As quoted from wikipedia..
For example - People may use /j to indicate they are joking, or /ij to indicate an inside group, between friends or members of a community. /s can also be used for sarcasm, something that for some can be quite hard to detect over the internet, or /q to indicate someone is asking a question. Here are some more examples -A tone indicator is a symbol attached to a sentence or message sent in a textual form, such as over the internet, to explicitly state the intonation or intent of the message, especially when it may be otherwise ambiguous.

Overall, I think this is a really clever and useful idea that has developed, and hopefully this lil artcle helped some more people understand what on earth these tags mean, and how to use them to better convey the meaning of your messages

