Not just that, but some e-mail systems (Gmail comes to mind) have taken to hiding the signature underneath a little expando-button. You don’t see it unless you go looking.
If you are traveling for a work-related conference or business trip and have limited access to email, let people know in the body of the message. This shows that you are active in industry circles and that you’re dedicated to learning and serious about your professional development. This will win major credibility points in the eyes of your email inquirers.

I used to work with someone who had a message telling people she only checked her email twice a day. You pretty much needed to call her if you needed anything outside of those times. (She worked in a remote office.) I think she had read one of those books on efficiency that recommended scheduled email time. But there were problems with this: 4. My department often had to email attachments or text to illustrate our questions/concerns. And we were on deadlines. Reading a page of text over the phone was not an efficient use of anyone’s time 5. She did outreach & was often out of the office on site visits, trainings, or travel to these places, but never ever set her OOO for these, because she was “working.” However, she was effectively not available to read emails from other staff until after hours on those days.
Thank you for your email! I am on vacation. Vacations are not for checking email, so I won’t be doing that. Fortunately, we rarely encounter life and death situations in the world of [INDUSTRY TYPE], and aren’t we all glad for that? If you think I’m checking email because you just received an email from me, that is only because I figured out the pixies that send emails on a schedule. Really, I’m not checking email.