On the Internet, what is a dead giveaway that someone is actually a kid?

I know far too many people in their 40s who do this.

The way I try to reinforce the difference with people is this mnemonic device:

You don't want a loose noose - or you might lose the extra 'o'.

I associate this with boomers more than kids, but that's subjective since an old former friend I know always used to do it.

They also used "seen" instead of "saw", as in, "I seen dark clouds so I closed the windows." which is like nails on a chalkboard to me.