Linksys WTR54GS v2.1

Overview
WTR54GS v2.0 and v2.1 devices probably have serial numbers starting with SJH1 (or maybe SJH2).

OEM SerComm (T600A-1.0MM)

Links of Interest
WTR54GS on the DD-WRT wiki
 * On the DD-WRT forums

WRT54G series on Wikipedia