Where to modify Signup call-to-action content text

I think @riking implied to have you put his code snippet into the install’s head from the admin CP where you can directly edit the html.

It is a quick JavaScript edit and now I see why he said it was client-side. It renders from the client, not from the server that a plugin would do.

Paste between the <head>...</head> HTML tags where I surmise other JavaScript already resides.