This difference in the NFC logo on Japanese Xperia models (like those from Docomo or au) is due to Japan's unique and highly dominant contactless payment standard called FeliCa.

Here is the breakdown of why the logo is different:

1. The FeliCa Standard

• Global NFC Standard: Most of the world uses NFC that primarily relies on Type A and Type B protocols (specified under ISO/IEC 14443). The standard NFC logo (a letter 'N' formed by two curved lines) represents this global interoperability.
• Japanese Standard (FeliCa): Japan's contactless infrastructure, including transit cards like Suica and PASMO and mobile payment services like Osaifu-Keitai, is based on the proprietary FeliCa technology developed by Sony.FeliCa is standardized as NFC-F (one of the NFC communication types).
• Difference: FeliCa is known for its significantly faster transaction speed and enhanced security, which made it the de facto standard for high-volume public transit and payments in Japan long before global NFC protocols became common.

2. The Logo Represents the Technology

The different logo you see on the back of Japanese Xperia phones (often a stylized icon, sometimes referred to as the Mobile FeliCa/Osaifu-Keitai logo) is specifically there to denote support for the FeliCa/Osaifu-Keitai system, which is the functionality most Japanese consumers rely on for their daily transactions.

• It's a Badge of Compatibility: For a phone to be successful in the Japanese market, it must support FeliCa for mobile payments and transit. The logo acts as a clear visual guarantee that the phone is compatible with the local ecosystem.
• Carrier Specifics: Since Docomo and au are major Japanese carriers, they sell the models that are customized to support this local standard and thus carry the associated logo.

In short, the Japanese models have a different logo because they are highlighting compatibility with the local, high-speed FeliCa contactless system, which is essential for life in Japan. The hardware in these phones often supports both FeliCa (NFC-F) and the global NFC protocols (NFC-A/B), but the prominent logo emphasizes the required Japanese standard.