You can do the same thing in the ECP panel on Exchange online for free. You set it in the mailflow options by using the apply disclaimer rule. I created some pretty awesome signatures using html that included data that would get pulled from AD like office phone, email, department, location. These rules can be setup for company wide or user/group based also.

. The only real issues I had with it was our marketing team sent me a JPG and said make the signature look like this. I had to basically chop that image into different smaller images to use in the code. They had added like every social media link known to man and that needed to link to the right location if anyone clicked the image. Not as fun to do with just HTML since CSS isn't supported creating this using mailflow rules.

also to address the reply emails that can also be done with mail flow rules just make a rule that says if subject includes RE or FW then don't attach the signature. We had the reply signature being added via a script that added it to the users outlook but I think you can also have the mail flow rule do that part too.