Disks of plastic or titanium or something, stamped and uncounterfeitable.
"Space Viking"
Henry Beam Piper
295. If the liquefied gases are used, the form of the iron furnace must probably be changed, and perhaps it may be necessary to direct the flame from the ignited fuel upon the ore to be fused, instead of mixing that ore with the fuel itself: by a proper regulation of the blast, an oxygenating or a deoxygenating flame might be procured; and from the intensity of the flame, combined with its chemical agency, we might expect the most refractory ore to be smelted, and that ultimately the metals at present almost infusible, such as platinum, titanium, and others, might be brought into common use, and thus effect a revolution in the arts.
"On the Economy of Machinery and Manufactures"
Charles Babbage
Perhaps, in the plans for the new cities of Pittsburgh and Chicago, we have sign of the social titanium that will increase the tensile strength of democracy in the places where the stress and strain are greatest.
"The French in the Heart of America"
John Finley