Standard Insight Communication cable boxes are not capable of displaying subtitle information, but the cable box and DVR combination units can. The subtitles are a feature called closed captioning, and are meant for hearing-impaired users. They are also useful for reading information on the screen while the TV's volume is muted. You can turn off the subtitles through the User Settings menu.
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Turn off the DVR.
Press the "Menu" button on the remote to display the User Settings menu.
Highlight the "Closed Captioning" field and press the left or right arrow button on the remote to select "Disabled."