Maybe you haven't tried this yet; John Carter to the rescue! "There have been times when I was responding to someone’s question when I really wished I had a template with a stock answer.
"Well, it’s really easy to do. There are two ways to do it. One is using a Signature, and the other is using Stationery.
"Using a signature is easier to work with if you need to edit the content. I have discovered that if you are using Stationery, it’s more difficult to edit the content. In fact, it appears to be impossible. It’s just very difficult. I’ll explain how to create both. The amount of detail below is for beginners." And here we quote John in all these directions:
Using a Signature:
Create a new message. It can contain images. Whatever you put in that message, including how it appears, will show up in the new signature.
Select the entire body of the message, including your actual signature - if you put one there. (Cmd-A)
Copy the selection to the clipboard. (Cmd-C)
Open Mail->Preferences. (Cmd-,)
Select the Signatures tab in the toolbar.
Make sure that the left side panel is showing “All Signatures” and click on it to make it active.
Click on the ‘+’ sign under the center panel.
Change the name of that Signature from “Signature #x” (where ‘x’ is a number) to something you will recognize.
The right side panel may or may not contain something.
Click inside the right side panel and paste the content of the clipboard. (Cmd-V) If there was something else there, just do Select All (Cmd-A) followed by Paste (Cmd-V) and it will be replaced.
In the left side panel, leave the “All Signatures” selection active and scroll down to the e-mail account that you want to add the new signature to. Do this without clicking inside that panel. Instead, just hover the mouse pointer in that panel and scroll down. (Using the Magic Mouse, slide your finger up and down the center. Using a mouse with a center wheel, move the wheel back and forth. If you have neither, click and hold the scroll bar on the right side of the panel to move it up/down). The center panel should still be showing the signatures (by name).
With the desired e-mail account in view, click and drag the new signature onto the e-mail account.
Check the bottom part of the Signatures window and note what “Choose Signature:” contains. If it is blank, that means no signature will be added to your e-mail messages. It doesn’t matter in this case - you don’t want it to show the new signature unless you want every message you start contain that signature.
Also note the box for “Place signature above quoted text.” If checked, your signature will appear above any message you may be replying to or forwarding. If not checked, it will always appear below any message you may be replying to or forwarding. If you are not replying to or forwarding a message (you are creating a new message), there will be a blank line above the signature in your new message.
When you start a new e-mail message, you should see “Signature:” on the bottom right side of the message header. Click on it to show all the signatures and select the one you want to show in the message. Whatever signature is selected will automatically appear in the body of the new message (even a message that you are replying to or forwarding).
Create a new message. It can contain images. Whatever you put in that message, including how it appears, will show up in the new Signature.
Click File->Save as Stationery.
Give your new Stationery a name and click “Save.”
Stationery is intended to be a background and/or template to a new message. You cannot use Stationery in a reply to, or forwarded message like you can with a Signature.
If you put text in Stationery at the time you create it, it shows up in a text box and you are expected to click anywhere in that text box to change the entire content. To edit the content is not impossible, but requires patience while you move the text cursor around with the arrow keys on the keyboard. For any other prepared Signatures, you can place the text cursor anywhere are start editing. To create a Stationery like that requires more detailed instructions - which are available online.
For Signatures that I have created containing text, as soon as I select any part of the text, the entire text is highlighted, including any images I placed there. It is impossible to place the text cursor anywhere in the text such as to select a word. Once the entire area is highlighted, if I want to edit any part of it, I have to use the arrow keys to move the text cursor around, and it always starts at either the very beginning or the very end.
My choice is to save a template as a Signature. Any part of it can then be edited as you would normal text.
And so, that's John Carter's lesson for today.