Auxiliary handstamp, SPECIAL DELIVERY
Special Delivery was available for some classes of mail at an extra fee beginning in 1885. Postal clerks used this marking device to apply a "SPECIAL DELIVERY" endorsement on the front of the envelope, usually above the addressee name, when this extra service was purchased.
First Class mail with a Special Delivery fee covered by postage stamps could be deposited in any mail box. These mailed items might receive this marking at the destination office by a distribution clerk. Otherwise, the sender might apply their own auxiliary marking specifying this service or write "special delivery" on the front of the envelope.