| Trefoil Warning Sign with Straight Arrows between Blades (late 1940s) |
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| The use of arrows between the three blades of the symbol seems to have originated at the Public Health Service in the late 1940s. |
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Last updated: 07/25/07 |
| Trefoil Warning Sign with Straight Arrows between Blades (late 1940s) |
|
| The use of arrows between the three blades of the symbol seems to have originated at the Public Health Service in the late 1940s. |
|
Last updated: 07/25/07 |