Choice of symbol has some degree of being arbitrary and I only preferred '@' for when because we (at least in USA) often specify time that way. E.g. "meet for lunch @2:00pm". However, I can see that '@' might feel like a fragment of an email address John@xyz.com.

The tilde '~' because UNIX/Linux alias for user's home directory. Hence the "who". I do admit that's a meaningless reason for any mainstream audience.