Must be a synonym of the company or the product it represents
A logo accurately designed is the company presentation card: there is no conjecture about the kind of companies or the activity they carry out when we see a logo that says American Airlines, Microsoft, Toyota, etc. This way everybody is immediately identified.

Must penetrate peoples mind as a selling agent
If a company has a high quality product, it is immediately demanded by the consumer society. Then, consumers look for the logo of the product or company before acquiring the product to assure they are buying the brand they were looking for. Companies such as Benetton, Nike, Reebok, etc. make sure that their logo appears on every ad so that the consumers become familiar to them and they always expect to see these marks on their goods.