How to identifiy incentives for one transaction

Hi,
if a user choose an incentives, how can i identify which one he chooses.

it cannot be identified by the funding amount, as
1. the user can decide not get an incentives
2. the user can fund more money as required by the incentives
3. there can be two incentives with the same funding amount.

we didnt find any hints in the database.
please advise. thanks.