Trademark

A logo becomes a trademark, whenever the logo is used explicitly to identify a particular ware or product.

Trademarks are mostly used to stay in the mind of the customer. The goal is to be silhouetted against competitive products.

 

In order to become a trademark, it needs to be registered according to trademark law. The trademark may be a character or glyph, or a combination thereof.

To summarize: A logo is mainly used for companies, while the trademark is designed for a company's products.