This character is a Other Symbol and is commonly used, that is, in no specific script.
The glyph is a square composition of the glyphs Latin Small Letter C, Latin Small Letter M. Its East Asian Width is wide. In bidirectional text it is written from left to right. When changing direction it is not mirrored. U+339D offers a line break opportunity at its position, except in some numeric contexts.
The Wikipedia has the following information about this codepoint:
A centimetre (international spelling) or centimeter (American spelling) (SI symbol cm) is a unit of length in the International System of Units (SI) equal to one hundredth of a metre, centi being the SI prefix for a factor of 1/100. Equivalently, there are 100 centimetres in 1 metre. The centimetre was the base unit of length in the now deprecated centimetre–gram–second (CGS) system of units.
Though for many physical quantities, SI prefixes for factors of 103—like milli- and kilo-—are often preferred by technicians, the centimetre remains a practical unit of length for many everyday measurements; for instance, human height is commonly measured in centimetres. A centimetre is approximately the width of the fingernail of an average adult person.