I want/need to use the word 'Android' referring to the Android-System/Software in a paper/thesis. I found these guidelines. Do I have to use both, the TM-symbol AND a footnote? Like AndroidTM - It looks strange...
Your thesis or paper is in this respect similar to a newspaper article about the product ("Independent coverage"). Do newspapers use the "TM" symbol if they write about products? No. (At least no newspapers or magazine I know does.)
It is used by people who have an agreement, are cooperating with the proprietor of the brand name in question, to show exactly that.
These "guidelines" (same as e.g. Microsofts EULAs etc.) are not even a binding contract in many legislations, because they try to force them on you after you have already paid for the product.
I would advise you to be as conservative as possible and err on the side of adhering to the wishes of the trademark's owner. It won't do you any harm, whereas breaking a rule/convention might wind up giving you grief.
The rights of owners should be respected, especially when the cost is essentially zero. You will want them to respect your IP in future as well.
It is easy to Do the Right Thing when it costs you nothing.
I would guess, however, that mentioning the trademark and its owner once in the paper is sufficient.
And note that you do this, not because of a legal threat but because you respect the people that built the system. This is especially true if their prior work has enabled your own.