Those look like the same letters that are on my 1985 tailgate finish panel:
Ford used these same letters on the grille of L- (800 - 9000) series.
Lucille: 1985 Ford F150 XLT Lariat
*Colors: Dark Canyon Red exterior, Canyon Red interior
*Engine: 5.0, CompCams 31-230-3, "Thumper" E7 heads, Edelbrock Performer intake, Autolite 4100 carburetor, DuraSpark II ignition, Thorley Tri-Y headers, Flowmaster dual exhaust, H-pipe.
*Drivetrain: AOD transmission, 3.55 gears, 2wd.