Unfortunately that's not under control of those businesses. This plain text email you sent comes across with clickable mailto and http links in your signature in most modern email clients despite you having sent it in plain text. "Helpful" email program defaults won't force people to copy and paste the URL. They just create the hyperlink for people based on the pattern in the plain text message. It seems anything beginning with www or http(s):// will be converted to a clickable link out of convenience to the user. It's always that endless struggle of security vs. convenience...
At least it is what is says, and the effect is precisely the same as if one copied and pasted the link into the browser. What is truly evil is non text/plain email. Anyone who permits or assists in the rendering of non-plaintext email deserves whatever befalls them -- and they should not be permitted zero-liability for their stupidity and ignorance. They end-user is of course entitled to cross-claim against the manufacturer of the defective system or device which rendered the message in a deceptive way (such as Dell and Microsoft in particular). --- () ascii ribbon campaign against html e-mail /\ www.asciiribbon.org