| 1931 RICHARDS Signaling Apparatus Patent Print |
| 1931 MCCANN Railway Signaling System Patent |
| 1931 WESTERN ELECTRIC CO Signaling Device Patent |
| 1931 BUTLER Electric Signaling Apparatus Patent |
| 1931 LOYAL SCOTT Signaling Device Patent Print |
| 1931 YOUNG HENRY Railway Signaling Patent Print |
| 1931 BROOKS CHARLES Railway Signaling Patent |
| 1931 BUTRIDGE Railway Signaling Apparatus Patent |
| 1931 GILSON Electrical Signaling Patent Print |
| 1931 DUFFY Signaling System For Railroads Patent |
| 1931 PARRILL EASTON Railway Signaling Patent |
| 1931 HOFFMAN Railway Signaling System Patent |
| 1931 MCCOLLAM CLARENCE Signaling Device Patent |
| 1931 PENROD Railway Signaling System Patent |
| 1931 WIGHT Signaling System For Railroads Patent |
| 1931 DOVER SAMUEL Signaling Device Patent Print |
| 1931 HARTLEY Railway Signaling Apparatus Patent |
| 1931 SCOFIELD THEODORE Signaling Device Patent |
| 1931 DICKE Signaling System For Railroads Patent |
| 1931 PLATT HARRY Signaling Device Patent Print |