Sequence logos are created from collections of aligned sequences and consist of stacks of letters representing individual positions in the sequence alignment. The height of each stack indicates the sequence conservation at that position of the alignment measured in bits, and the height of each symbol within the stack reflects its relative frequency at that position.
Sequence logos can be created with tools called sequence logo generators, or sequence logo makers. One such tool is the Sequence Logo Kit. It is browser-based, fast, and highly configurable.