Record which timeline created an activity
This is more of a workaround but you can create activity types specific to each timeline and then include the name of the timeline in the activity type label, e.g. if you have timelines named A and B then you could have activity types labelled:


A - Phone Call
A - Fill out requisition
...
B - Phone Call
B - Fill out requisition
...

Alternatively the add timeline feature will create dates relative to whatever offset you have in your config for that timeline, so you could have an "anchor" activity type which you create just before you add a timeline, and then in the timeline config you say make the offsets relative to that activity type. You'd have to rejig your timelines to match that workflow.