Numbers for call letter signs?

[Bob Nelson]

Noticed the following listed on 100000watts.com's
Burlington/Plattsburg FM page:

48691
88.7 MHz  Format: cp-new
Licensed: Rouses Point, NY

78628
90.9 MHz  Format: cp-new
Licensed: Schuyler Falls, NY

Probably translators, yes, but is this how call
"letter" signs are being issued for them? All numbers?
(or maybe that's just a reference number for the FCC
database, for each station?)