Are iframes much slowing ?

Hello,

I just post here because I noticed that a few members have what they call "coded signatures", which are iframes integrated in their signatures so they can show plenty of things with a nice layout.

I have nothing against these signatures but I was wondering if iframes get the pages much slower ?

As well, what's better between an iframe from a page of my own website and an iframe of a page hosted elsewhere ?

Many thanks for your help !