Well, you can keep things simpler and just fill in the hidden source field on the form as per the UTM source values (assuming you have a proper UTM strategy in place). Check out the product documentation on setting a hidden form field on the Experience League. As an alternative, you can update the source field via a smart campaign, but you'd still need apt constraints (such as query string) to ensure that you're able to accurately stamp the source value, e.g., you would not want to attribute all the form fills on this page to paid search, so you need differentiators (like apt UTMs) to tag the correct source value. You might also want to put apt field blocks on this source field so that once written, it can't be updated (some users also maintain 2 source fields - Original and Last source fields - the former holds the source of the first interaction and the latter holds the source of the last, i.e., the recent most interaction). You can further use the source value to add people to the apt Salesforce campaign (if you have source-wise SFDC campaigns in place) via the Add to Salesforce Campaign flow step in Marketo.
.png)