What you've been told is true.
The entity (℠) only works well in some browsers. IE 8 and less show an empty square. Others may show a ? or other placeholder symbol. Opera renders it, but it's virtually illegible. Chrome and IE 9 are good, Firefox probably is too, depending upon the OS and browser versions. Chrome might have a problem on older systems. I tried pasting in the literal character, same results.
So I guess you're stuck with <sup>SM</sup>, as inelegant as it appears. It can be styled to look a bit more presentable. Like with this in the stylesheet:
Code:
.servicemark {
font: normal 65% sans-serif;
}
and this for the markup:
HTML Code:
<sup class="servicemark">SM</sup>
Still a bit off in IE 7 and less. You could use conditional styles to tweak that. Or, those browsers are on the decline. Most folks have at least IE 8. It doesn't look horrible in IE 7 and less, so you might just let that slide.
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