@mwalker973 This is the approach I would recommend:

Have all your Signup Forms all submit to your primary List - let’s use your example as the “Newsletter” List. Then to differentiate between the various Signup Forms, you provide an additional value to the $source value. Then trigger a different Flow for each Segment (to send the first email that’s related to that Signup Form) and let the Newsletter List Subscription handle the following emails in your Welcome Series.

In the Signup Forms, you can specify the $source value like this:

Then create a Segments from your Main List based on each Signup Form’s $source value:

And then you can create a Flow triggered by each Segment:

Simply repeat this process for each $source.  Everyone will be in your Main List where they can get other emails in your Welcome Series.

Hope this helps!

@mwalker973 What if the person is already on the list? Will the new sign up override any older source property value and correctly trigger the flow?

@retention, love this solution!

Building off of what Retention had used as an example, @JimmieaQuick, if the contact was already within the “Newsletter List” but signs up for a new form, their “$Source” property would indeed update! This would allow the contact to be caught by the correct corresponding Segment and served the flow despite already being an existing member of the “Newsletter List”. 

Keep in mind though that List and Segment triggered flows can only be served once to a contact! This means that contacts who have previously gone through one of these Segment triggered flows by signing up to a form, they would not be served this same flow a second time should they fill out the same form again. 

-David