Q: In preview how do I delete signature?

I am a bit confused... as you may be in stating what App you are using?

Also, when you say "... my signature ..." I will assume that you mean and image of your signature in some format, .jpg, .png, .tif, etc.

Preview is pretty much a read only (you can 'Crop' an image) - 1 layer - image editor that will also view PDF files.

TextEdit on the other hand is a text editor that will accept inline images, just like the compose window that you used to post your question and I am using to reply.

If indeed you are using TextEdit, I cannot even begin to recreate your issue. I can however suggest a workaround...

Select All > ⌘ Command + Click the image to DE-select it from the 'All'

Copy

[File] > New

Paste

This should result in a new document with all BUT the sig image

CCC

You have either not updated your profile or, if it is correct, then the newer version of Preview would not run on it. It depends on which version of Preview you are running; the newer versions all allow signatures as well as several notation/editing features:

Preview 5.x: Sign a PDF document

If you are running Preview 5.x or higher, it also includes directions on how to delete it.

Just had this issue. 

Worked for me:

File --> Revert to --> Previous save

I spent all afternoon trying to figure out how to do this!  I was finally able to remove it using Adobe Acrobat in another computer (running Windows) and manipulating the images.  This is how I was able to do it:

1. Open the document

2. On the right-hand toolbar, choose "Images"

3. Mouse over to the page with the signature in question (but not the signature itself) and click on the text. A blue outline should appear on the entire page.

4. Grab the bottom square in the middle of the outline and move it upwards.  You will see the entire text of the page move upwards, but not the signature.

5. Once the text is above the signature image, you should be able to select it by clicking.

6. Once image is selected, you should see the blue outline with the little squares around it. Delete the image by pressing the "delete" key or selecting "delete" from the right-click menu.

7. Bring the text of the page back down to its original position.

It seems what happens when one places a signature image on Preview, that it moves it to the background once the document is saved.  Adobe Acrobat allowed me to move the image in front of the signature so I could get to it.

Hope it helps!