If you are writing a manual that mentions products other than your own, pay attention to the brand names. They might require a trademark, which you have to mark with a symbol.
The two most important trademarks are:
Most trademark symbols should only be used when you mention a brand or product name for the first time. Online texts (for example in a webhelp) are more difficult, because readers sometimes happen upon the manual on a random page. To be safe, it is best to always use the symbol, for example using a conref.
DITA Tip: DITA has a dedicated <tm> element to mark up trademarked names. All you need to do is wrap the name in a <tm> element and select the correct type of trademark (TM or registered), for example:
<keyword id="keyword_t2d_2rs_lcb"><tm tmtype="reg">Bluetooth</tm></keyword>
If you don’t know whether a product or brand name has a trademark, you can usually find the answer on the brand’s legal pages.