You should only use fonts that are generally available across different operating systems. Otherwise your signature may not appear as intended when people receive email from you. This is because fonts are not embedded.
Generally, in email signatures it is recommended to use fonts such as Calibri, Arial, Verdana, Georgia, Times New Roman, and Courier. These fonts are often referred to as web safe fonts.
Most email clients do not support web fonts. If you use a web font that the receiving email client cannot display then it will be shown using a fall back font. This will usually be Helvetica, Arial, or a generic sans serif font.