The creation of the Universal Postal Union spurred a competition among those countries that thought their postage stamps could be more beautiful, and, in fact, actually do more than those of other nations.

Dial Pressure Stamp

This Haitian 5-centime measured the p.s.i. inside an envelope to warn recipients of contents packed under pressure.

Dial Norton Stamp

Another cautionary issue, the Netherlands’ 5-gulden stamp indicated the voltage of a letter, using the classic Norton Voltmeter.

Dial Compass Stamp

The New Zealand 4-pence included a working compass for those traveling with the mail.

Dial Radio Stamp

The Malta 2-pence “Silvertone” brought in radio stations from all over the world.

Dial Safe Stamp

The short-lived U.S. 10-cent “Safe Lock” stamp offered remarkable security, but unfortunately senders often included the necessary combination inside the letter, thus locking out the recipient who had to visit either the Post Office or a locksmith to gain access.