In Japan, there is no law regarding virtual marking.

Japanese Patent Law, Article 187, requires marking but there is no penalty for failing to mark. It is possible to enforce a patent right even if marking of patented products has been omitted. Therefore, in effect, there is no requirement to mark. However, as a practical matter, marking may help to avoid innocent infringement defenses in patent litigation.

Under the Japanese patent law, false marking is prohibited (Article 188). Further, any person violating Article 188 shall be subject to imprisonment with labor not exceeding three years or to a fine not exceeding 3,000,000 yen (Article 198). Accordingly, if there is marking, it is necessary to pay attention if a patent has expired, has been deemed invalid, or has been abandoned for failure to pay a renewal fee.

If you choose to mark in Japan, the marking should consist of the word “Patent” and the patent number.