Hey there! 

The best option would be to use UTMs at the end of your URLs and have a hidden form field grab them. 

Say you're running a Facebook ad; you can add a UTM parameter to your ad's landing page URL. In the below example, the campaign source will be captured along with a form submission: 

http://try.unbounce.com/join/?utm_source=facebook

If you'd like to track more than just the source, you can add more URL parameters by separating them with an ampersand (&):
http://try.unbounce.com/join/?utm_source=facebook&utm_medium=social

This way, if a visitor clicks through your ad on Facebook, and completes the conversion action on your Unbounce landing page, the parameter value will submit along with the form submission.

This document here goes over it all! https://documentation.unbounce.com/hc/en-us/articles/115005751566-How-do-I-track-referral-sources-for-my-campaigns-

Is there any way, short of manually coding the links with UTMs, to look at an Unbounce landing page in Google Analytics and see where the traffic came from?

Hey @Stats888, 

For your Google ads, you can look into auto-tagging for your pages which should show up in Analytics. For other traffic sources, setting up UTMs as Kevin outlined above is the best option that I’m aware of. 
 

There may be a new option that shows up as GA4 progresses!