A shield is a medieval symbol that was used to represent the knights and their coats of armor. From then on, the symbol has come to stand for nobility, protection, balance, harmony, growth, hope, strength, and learning. A shield also represents well-being, loyalty and commitment.
This is why a shield is often seen in logos that need to reference some kind of fraternity. You will find the shield symbol in the following type of businesses and institutions:
University and College: University, college and school logos use the shield or crest in their logo. This is to provide a reference to the nobility and learning doled out by the prestigious institute.
Clubs: Club logos need to appear exclusive and esteemed. Incorporating the shield symbol, either as a crest, or as a partial element, creates an immediate sense of exclusiveness and respect which the club logos require.
Security Company: Security companies especially those in tech and science businesses can also use the shield in their logo to represent security, protection, growth and prestige.
Motorbike: You will also see the shield appearing in motorbike logos –mostly because bikers like to think of themselves as part of an exclusive fraternity, and a shield symbol conveys that idea well.
A shield can also be used for many other industries. If you feel it might be appropriate for your logo, try out some options through designmantic's logo creator software which allows you to tweak multiple options and explore many templates.