Petition signature doesn't show as an activity type for scheduled reminder

On dmaster, if you look at activity types, Petition Signature is Activity Type ID 32. However, if one attempts to use the creation of an activity of that type as the basis of a scheduled reminder, it doesn't show up in the list of types of activities, even though it should. So the objective is to be able to send an email as a scheduled reminder 2 days after a petition is signed, which should be possible when the list is expanded to include this activity type.