Written by: Laura Swords
Laura Swords is the founder of SwordsNet Designs, which provides web and graphic design solutions for small to mid-sized businesses. With over 20 years of corporate experience in both the IT and marketing arenas, she possesses the unique combination of technical and creative skills.

I tried the Spark workaround and am happy to report that it works. It's BS that Apple can't make this work on their own, but I'm glad we have a temporary solution.

To recap:

1) Download the Spark mail app

2) Open the app, go to Settings, and create your signature in the Spark app

3) Create a new email in the Spark app

4) Copy the signature from the Spark email

5) Go to your iPhone/iPad Settings -> Mail -> Signatures

6) Paste in the signature you copied from Spark

7) Shake your iPhone/iPad to undo the formatting change

8) Go to the Apple mail app and open an email to confirm it worked

Voila, worked for me. Thanks to the person who found this. Get your act together, Apple!

I ended up using the recommendation from a few weeks ago about using the Spark App and it works.

At first I thought that every time I wrote an email I would have to paste the signature but this is not accurate.

Follow the last instructions for Spark. Sign up using any email and create the signature with the logo you want. Close out the Settings of Spark and create a new email. Copy THIS data and paste it into the signature of the Apple Mail settings.

In the Spark Settings, I set "San Francisco" font to 13 I believe so it was the same size as the Apple text.

Also, I have successfully done it without shaking to "Undo Attributes" .....

So just to confirm, I DO NOT have to paste the signature from Spark every time I create a new email. The image is there, it does not say "Null" or a blank box.

I'm not going to update this phone again until someone says this issue is fixed because I do not have any other issues!!!

I've spent hours chatting with Apple tech support about this issue for a new iPad Pro. They referenced remedies in this thread, but eventually told me the feature is not supported and suggested I try another email client.

***Please Read Carefully***

there is obviously something that has broken in iOS 13 regarding HTML signatures. Here is the fix for your mail app.

download Spark (you will be using this to create your signature only).
copy and paste the target signature into the spark app. You may or may not need to shake to undo attribute changes.
open a new email in spark and copy the signature that you just created from the new blank email.
paste the signature from the spark email into the signature for your iOS mail app via settings.
you can now delete spark and you should have a working signature. I literally just did this 5 minutes ago.

My HTML email signatures are created in an App Store App called "Email Signature Creator" and work fine with ios13. I did have some problems initially (which is how I found this thread), but after selecting "Load Remote Images" in iOS Mail settings, all worked perfectly normally (as per my comment near the very start of this thread). I'm not sure whether "Email Signature Creator" is doing something similar to what some users have found with "Spark", but I can definitely say that I have HTML signatures (a different one set for my three different email accounts) and they work exactly as expected in iOS13, including calling on remote images for logos, etc.