Wind turbines are culturally identified with environmental stewardship, and a green, healthy future. So it is fitting that the Postal Service is celebrating Earth Day 2013 with a postmark depicting wind turbines.

Postage stamps pay for the cost of mailing. Postmarks cancel the the stamp for further usage and confirm that the postal service has reclaimed the cost of the postage.

Like postage stamps, postmarks have evolved over the years to convey not only the location and the date that the stamp was cancelled, that is, that the mail was received and begun its trip to its destination, but also as a form of cultural identification.

Postmarks can be more localized than postage stamps. For example, some local post offices could imprint the postmark with a message resonating with local users.

Private mailers in the USA can design their own cancellation messages, within certain guidelines, and when they postmark the mail on their own machines they can imprint the message.

Wind turbines and the sun symbol are two icons easily recognizable as symbols of environmental stewardship.

So it was appropriate that I recently received a letter from my mother postmarked Indianapolis, Indiana that celebrates Earth Day 2013 with an image of wind turbines and the sun.