You can hide an image on Advocate Signup/Share pages or Friend Claim page on mobile devices by following these steps:
1. Open Campaign
2. Navigate to Editor tab
3. Select Advocate Signup/Share pages or Friend Claim page view
4. Switch to the HTML & CSS tab
5. Find the following piece of code: <div class="content-mobile-image"></div>
6. Remove it or comment it out
7. Save changes