A trademarked logo means that the business or persons who own the logo have carefully designed it to be completely unique.
Applying for your logo to be trademarked is often best left to the professionals as a detailed search is required in various categories to investigate whether your logo is indeed unique or differential enough from other logos that have previously been trademarked.
Copyrighting your logo means that no-one is allowed to create any copies or derivative forms of your intellectual property. Think of you logo as a famous painting – no person may make a copy of it or try to make their “interpretation” of it without your permission. If they do, you will be able to take legal action against them if need be, but generally a simple email detailing your grievances will suffice.
When having a logo created by a graphic designer or even a friend – one should have a clear contract in order to determine who’s intellectual property the logo will become once the work is completed. A designer may grant you the rights to use the logo, but may detain it as their intellectual property and it is important to ascertain these details beforehand. Generally when one pays for a service – in this case the creation of a logo, it will become yours – however these details need to be clarified before the logo design commences.
Granted that not all individuals and small business owners will have enough money to apply for their logo to be trademarked and often having their logo copyrighted is good enough – provided you have not infringed on any other persons or companies intellectual property.
Often large business will do both – they will register their logo as a trademark and copyright the symbol, text, colours and so forth as well. This is rightfully necessary as they may need the intellectual property protection more so than a very small, one man business.