Proper use of "TV"

It seems "TV" is always preferred when used as an abbreviation for "television" in informal writing, but is "tv" ever acceptable? (The capitalization seems to me to place undue emphasis on it.)

Upper case has the advantage of making it clear that the letters are an abbreviation rather than some kind of weird word. And it isn’t just TV. Upper case is often used for other abbreviations, even when upper case is not necessarily used for the full form. For example,

CD (compact disc)

DVD (digital versatile disc)

SIM (subscriber information module)

ATM (automatic teller machine)

ENT (ear, nose and throat)

GDP (gross domestic product)

RPM (revolutions per minute)

BIOS (basic input output system)

Lower case initialisms are found, but capitalising is by far the more usual. Lower-case tends to either be because it relates to a case where there are standardised lowercase abbreviations (kmph, km/hr & mph) or when the initialism moves toward being perceived as a word rather than its origin as an initialism (LASER and SCUBA becoming laser and scuba and even having back-formations like lase).

Using an unusual form like tv would give it too much emphasis to my mind.

The form teevee I personally dislike, but it is found and there's no technical reason to object. That said, it's been in use since at least the 1950s but nowhere near as much as TV, so it doesn't seem like it's ever going to be anything other than rare.

"TV" is an initialism — an abbreviation in which we say the name of each letter. Although there are some exceptions, initialisms are usually written in upper case. This helps the reader understand that it is an initialism.