Written Japanese has three different scripts — hiragana, katakana and kanji — so you wouldn't think there'd be room for any more. But you'd be wrong.
ローマ字 (rōmaji, the Roman alphabet) is often considered the fourth Japanese script, and has carved out a space for itself in everyday life. For example, recently it popped up in the name for the Tokyu Oimachi Line's new seat reservation program, Qシート (kyū shiito, Q seat). The letter "Q" is meant to stand for the English words "quick" and "quality," and also provides an alliterative link with the 東急 (Tōkyū, Tokyu) Corporation that operates the line.
Other common made-in-Japan acronyms composed of English words include OL (ōeru, office lady), which is a female office clerk or secretary; and LDK (erudiikē), a combined living-dining-kitchen area in a house or apartment. More colloquially, NG (enujii, no good) can be used as an expression of disapproval, to indicate that something is not allowed. Although made up of English words, some Japanese are still surprised to learn these terms aren't that familiar to English speakers outside of Japan.