Tian, ??He and Si are Chinese characters and can appear on trademarks. The following are some common situations where the words Tian, ??He, and Si may appear on trademarks:

1. Agricultural field: Tian, ??He, and Si are symbols of agriculture, so these words may appear on agricultural product-related trademarks. . For example, agricultural products may have the word "HE" on their trademarks to highlight their agricultural-related characteristics.

2. Agricultural machinery: Manufacturers of agricultural machinery and agricultural tools may use the characters Tian, ??He and Zui in their trademarks to highlight their characteristics and uses related to agricultural machinery.

3. Agricultural services: The characters Tian, ??He and Zu may appear on the trademarks of some agricultural service companies or online agricultural platforms to indicate that they provide agriculture-related services.

4. Agricultural product processing and food industry: In the agricultural product processing and food industry, the characters Tian, ??He, and Si may appear on the trademark to emphasize its characteristics related to agricultural products or healthy food.

Please note that the above are just some possible situations. The design and use of specific trademarks are related to brand strategy and company intentions, so specific situations need to be analyzed based on specific trademarks. If necessary, it is recommended to consult a professional organization or lawyer for relevant legal advice.