Just accumulating what I’ve got from the Defcon 28 badge and such:



tlstFCOnRFoofFioumYrgureoohrDOuntlon
Transcription of the arced text with the skull
2
Transcription of the text on the maroon background with either an 8 or ∞ symbol.
Xbaw maek wzme pgty zvxy izwk iwhk lnhy agrl rrlp fsis xadh uflx dsqh rzrg qegu itwb wveq aslo moii xmzx mvea rtil yekd lvks jrbo arvy nmjz wodi gcxe tkrr cyir xbsu rwyf slwr ixyk lrwz sbzr zbpg rrrw hjsi alXX 1o57
Here’s my first attempt at recording the cassette: