This is a label. It may also appear as 'CBS Records Masterworks', 'CBS Records Master Works' or 'CBS Master Works' on releases.
Label specialising in classical recordings, in use from the mid-1950s to 1990. Until 1980, the label was mainly employed in territories where the Columbia name was being used by the Columbia Graphophone Company Ltd., acting as a parallel label to the predominantly-US Columbia Masterworks.
Once Columbia Masterworks was renamed CBS Masterworks in 1980, all releases worldwide used this label until it was rebranded Sony Classical and Sony Masterworks in 1990 shortly after Sony acquired CBS.

However, some pre-1980 US releases exist which use the label. For example, between 1966 and 1969, some US Columbia releases were issued with blue CBS Masterworks labels, most likely to facilitate exportation into countries where the Columbia name was already in use. Some of these releases can be found in CBS-branded jackets, while others can be found with CBS stickers or blank stickers covering the Columbia logos.