Isn’t this the default behaviour when I highlight some text and select the “Quote” option? I can see in the post preview that the quote I selected is showing as “Elliot: just like e.g. earlier…”
Highlight the text you want to quote by clicking and dragging with the mouse, and then click on the Quote button.
Source: Forum Features Guide
Following that process results in the “lmf:” before, not after, the text lmf wrote.
Sorry, I thought that the way I quoted it and provided the source would make it clear it was not my writing. I will be more careful in the future.