Inserting a logo in email signatures

Logos in email signatures
I need to include a logo with address info as a picture file which will
appear on all emails from one company.
(It needs to be seen on Macs and PCs.)

Using a JPG looks ‘fuzzy’.
We need a format that is small MB size but sharp – so it looks
professional and text can be read.

All advice appreciated.
Many thanks,
Trant