There could be posters, displays in glass cases, materials at the alumni office, events at homecoming, etc. Decide what is best for your campus regarding specific actions tied to the Pledge. Have those taking the Pledge wear green ribbons, as might supportive faculty. Get one of the speakers to discuss or note the Pledge at the ceremony. Have the Pledge printed in the commencement program.
Different schools sign up people differently.
Another school has participants sign a poster, which is on display. Another has people sign a sheet after they have gone across the stage and gotten their diploma. Different schools have modified the Pledge wording to fit their own needs. Lead people to the web site or distribute such information to all graduates, Pledge signers, Career Services office, etc. Different schools recognize or celebrate the Pledge in different ways.