IOS 15.1 Mail Signature No Image or emoji

Signatures are all text. You will not be able to add emoji. As far as the default signature, is that the only one that you have configured? If you go to Settings>Mail, you can set it to All Accounts, or Per Account. With Per Account, you can create a signature for each account. I've checked my device, iPhone 13 Pro on iOS 15.1, and have the ability to edit all of my signatures. If you go to create an email from anything other than the Mail app, it will automatically select the default email account if that is where your problem seems to stem from.

I don't have a keyboard with the emoji icon on it either on the phone. I just checked my iPad Pro and cannot access the emoji keyboard there. While I've never used emoji in my signature, I cannot say if I could access emoji before, since I don't use that for my work Exchange email signature. The same for my iCloud mail account. I can say that the text box does look somewhat different since the last time I updated my signatures, so there may have been some changes. I use that in my work signature to make short announcements. I'm a college professor and will add a message to my signature like "college is closed" and the dates during spring break, and then the winter break, so I'm not changing things there often. I'm afraid that would be a question you may need to pose to Apple Support. I can remember from the beginning adding images and that has always been an issue, since the signatures have always seemed to be plain text and not HTML to support images.

I have always used emoji’s in my signature on my IPhone and IPad. I can no longer do this on my IPhone but I was able to still do it on my IPad. It was an additional step to add the emoji to my signature on my IPad.

I was able to get around this issue by using predictive text. I created a signature with emoji’s & then when into the settings/mail/signature & added the predictive text short cut & I then had my signature with emoji’s

Sorry I missed this reply and question. To address this to Apple, you use the feedback link, Product Feedback - Apple

Can’t get emoji on my signature either since the upgrade

You could have just used iOS and the iPhone, but they read all of the feedback and will get it to the correct area.