Spam link appears on mobile site only

I maintain a site that uses the Pinboard theme at http://heartlandconservatoryofdance.org. We’ve just learned that a spam link has started appearing just after the header image, in the

mobile version of the site only.

I found an old WordPress forum link about a bad plugin injecting spam into sites, so I disabled all my site’s plugins. That didn’t eradicate the spam link.

Since it only appears in the mobile view, I can’t view it in a browser that has a code inspector, meaning I can’t try to track down the section of the theme that might be injecting this. I can’t even find specifically how the mobile theme is generated.

Any advice? Thanks…