I'd like Emacs to display a big (but short) "pop up" text

[Marcin Borkowski]

Hi all,

I'd like to display a "pop up"/"tip", i.e., a short text (a few
characters).  The thing is, I want it to be visible: large font,
preferably centered on the screen.  My use case is demoing Emacs, and
before showing the effects of e.g. C-x 2, I'd like to show
a big-lettered "C-x 2" on the screen.  It would be nice to use something
like the blocks in M-x tetris to build the letters, or anything else
that would clearly show "C-x 2" or whatever keychord I'm showing.

Any ideas?

--
Marcin Borkowski