For a hyperlink just use www.facebook.com/++page ID++/like
Eg: www.facebook.com/MYPAGEISAWESOME/like
To make it work with m.facebook.com
here's what you do:
Open the Facebook page you're looking for then change the URL to the mobile URL ( which is www.m.facebook.com/MYPAGEISAWESOME
).
Now you should see a big version of the mobile Facebook page. Copy the target URL of the like button.
Pop that URL into the QR generator to make a "scan to like" barcode. This will open the m.Facebook
page in the browser of most mobiles directly from the QR reader. If they are not logged into Facebook then they will be prompted to log in and then click 'like'. If logged in, it will auto like.
Hope this helps!
Also, definitely include something with a "click here/scan here to like us on Facebook"