This is a sign representing the subway, which surrounds the letter "m" with a circle, and is common in the "subway" stations in urban areas. Different platforms display different signs, some depicting solid circles, and some displaying hollow circles. Except that LG and Docomo platforms display black letters and Google platforms display blue letters, the letters displayed on other platforms are all white. And the thickness of letter lines varies with the platform.
This emoticon can represent subway, transportation and daily travel.
