Paul, you're not going to find those on Wikitree, because they may not be Wikitree specific. For instance * can mean see footnote in non-wikitree. Or it could be being used as a bullet list on Wikitree (See Asterix). Sometimes in genealogy the plus sign + is used to mean look for more information on this person (usually below or in the following pages) or sometimes I use it in simple math equations. The tilde ~ is used for lots of things. On wikitree ~~~~ (four of them) will leave Your ID and the date and time, like a signature. Sometimes in old wills the ~ used over a word means some of the letters in the word are left out, a kind of 1600s short hand. I've never seen the two ~ on top of each other and wouldn't know how to create it. When you're stumped, ask, but make sure you let us know where you see it. What profile is it on? So we can see the context.
I think the ones Robert was speaking of are things like this 
If you find them on wikitree, hover over with your cursor and it tells you what it is.
