Which signifies the proper protection for locomotives against elements on track entries?

The proper protection for locomotives against elements on track entries is best signified by the placement of shields. Shields are designed specifically to protect locomotives from weather-related issues, debris, and other environmental factors that could interfere with their operation and safety on the tracks. By using shields, the locomotive can maintain better functionality and mitigate damage that would otherwise be caused by direct exposure to the elements.

Other methods, such as covering with canvas or installing alarms, do not provide the same level of protection from external physical threats. While guard rails are important for safety and preventing derailments, they do not directly shield the locomotive from environmental elements. Thus, shields are the most effective option for providing protection to locomotives when entering tracks.