All steel-string guitars have a truss rod. Most are adjustable, with the notable exception of Martins made before about 1980. Most inexpensive guitars and some higher-priced lines (Gibson, Guild, Taylor) have the adjustment at the headstock end of the neck and have a truss rod cover. Newer Martins and most small-shop guitars are adjustable via a hole in the heelblock accessed through the sound-hole. Click here for more truss rod info.