The symbol of the image means something really important, as it indicates the necessity of having a three prong electrical system, with earth. Earth means somewhere there is a ground rod —a piece of metal normally with a solid tube geometry— that is buried in the ground, with direct contact into the exterior surface of the planet.
The symbol could be printed somewhere in the appliance.
Electrocution could happen if a device with this symbol is plugged in an outlet without ground, a three prong outlet. Then it's extremely important not to forget what it means. A relevant question is, where does it come the risk?
An apparatus of this kind has conductive areas, specifically metal ones, that the user touches in a normal use. In a fault, a potentially lethal voltage could appear in those areas. Then, the user interface, called most of the time chassis, is earthed and this means that in a fault the electricity goes to earth instead of your body. Electricity tries to follow the least resistance path, or in other words, it prefers a cable toward ground to an organism that can conduct electricity but with difficulties.
If there's no other choice, because no outlet of this kind is available, the user must follow security measures. Wearing shoes made with non-conductive materials like rubber, avoiding a wet floor or touching the device with a wet skin are some of them. We recommend the use of stickers signaling the electrocution danger in the worst case if the device uses high voltages.
Sometimes, when you buy a product with this symbol, nobody warns you about an eventual electric shock. Be warned however!