Step 1: Stop the cursor at the position where you want to insert the trademark letters, and open the sogou input method.

Step 2: Right-click the input method and select the next menu "Symbolic Expression".

Step 3: After the "Symbol Collection" dialog box pops up, select "Special Symbol" in the list on the left, and drop the slider to the middle position on the right to find the registered trademark letter "?" , click the mouse to insert the specified location.