How do I display a userid in a post

[sys4096]

Hi There,

I would like to display the user's ID in a post, something like :

Hello there, you are user number : $userid -

e.g it would display for whichever user is reading the post in question.

I'm told there's a mod that enables me to do this but I just can't find it despite searching quite a bit here

Can anyone please help?

Cheers,
Paul.