First NFL team to use an insignia on their helmets?

In the first NFL season, there were 14 charter teams:

1. Akron Pros
2. Decatur Staleys
3. Buffalo All-Americans
4. Chicago Cardinals
5. Rock Island Independents
6. Dayton Triangles
7. Rochester Jeffersons
8. Canton Bulldogs
9. Detroit Heralds
10. Cleveland Tigers
11. Chicago Tigers
12. Hammond Pros
13. Columbus Panhandles
14. Muncie Flyers

Of these, the Canton Bulldogs were the oldest, and so are normally regarded as the 'first' NFL team.