Does a Logo Need to Explain What You Do?

[graceamelia]

My friend asked me last week whether her logo should clearly show what her business sells, or if a simple abstract shape was enough. It made me think about how many owners try to cram their whole service into one mark. A business logo design UK team would say the mark only needs to be recognisable, since the name and tagline already explain the service. A web design company UK team would add that the homepage does the explaining far better than a cluttered logo ever could. So I am curious, do you think a logo should show what you do, or just be memorable?