Yaki-niku means 'grilled meat', usually grilled on a hot plate, derived from the Japanese verb yaku 'to grill/roast/fry' and niku 'meat'. (Although niku is originally from Chinese, the word has been almost completely naturalised).
Yaki-niku is written or in Chinese characters, as in the following examples. The insertion or omission of the is optional, providing yet another opening for orthographic variation.
Of course, it is also possible to write the verb in hiragana: . And on some occasions the entire word can be written in katakana as , as in the following sign. In this case, the use of katakana harmonises with the rest of the sign, which can't be seen in this photo, in which most of the dishes are written in katakana.
A Google search in September 2003 found the following distribution for yaki-niku on the Internet. By way of comparison, the results for the similar form yaki-tori are also shown: