TL;DR: Add a banner to the top of the mobile site linking to the responsive site.
I regularly use the responsive site on my phone and occasionally, when I haven't been on a certain site for a while, or if I go onto a site I don't normally, I am presented with the mobile version of the site. It would be extremely helpful if a banner was added to the top of the mobile site linking to the responsive site.
Adding a banner to the top of the mobile site will encourage users who still use it to migrate to the responsive site, since the mobile site is being phased out. It will also allow users to switch to the responsive site quicker and easier; this is especially useful for users who struggle to find the little link located at the bottom of the site:
Here is an example banner: