3rd party e mail app for e mail signatures

Hi, I use a web mail service for my business and use i phone and Mac for day to day between business and personal. the web mail service does not offer an app and I wish to create a signature email for my business that works across all platforms, (Iphone e mail signature does not accept any images only text) so they would differ from device, is there a third party app that I could use across my apple devices with the ability to upload image and text for e mail signature?

Thanks in advance