The text engraved on the top is "MVS".
These dust covers are indented to go over the cart slot connectors on a MVS or CMVS system. They are generally the same width and length as a neo-geo arcade cartridge. But around a 1/3rd of the height. They are designed for vertical cart connectors and I can't guarantee the fit on a horizontal connector.
These are 3D printed from ABS plastic with an acrylic top with "MVS" engraved on top. Similar to how the original paper covers for the cart slots were covered when shipped from the factory.