Exchange Signature link to Instagram

Hi there london1976,

From what we can tell, you're asking how to add a link to your Instagram profile to the email signature for your Exchange account in the Mail app on your iMac. We're glad you've joined us in Apple Support Communities, and we can provide some guidance.

"You can use the Edit or Format menus in Mail to change the font or layout, turn text into links, or check spelling. To add an image, drag it into the preview area." Have a look at the 'Create signatures' section of this link to learn more:

Create and use email signatures in Mail on Mac

Also, you may find the information in this link helpful:

Change Signatures preferences in Mail on Mac

Cheers.