Let's suppose a mobile application aiming to suggest some meeting to others.
One user creates a Meeting (announcement) (without invitations) and some interested users can detect it in a list of suggested meetings and participate in.
Currently, the screen showing the detail of a suggested meeting is somewhat like that:
(for the sake of the example: [UserPicture] represents the real picture of the participant, not a textual link).
Of course, some of those participants may desist at any time and others may dare participating while hesitating all day long and without showing signs of life.
Thus, I expect each participant to confirm MANUALLY its participation, so that others (and the creator) could know precisely which are really expected/sure to come.
It would act as an engagement.
What is a good UX way to make the user confirm?
A button ? A green check ?
Where should I place the feature of participation confirmation?