DEAR ABBY: I was recently on a cross-country flight. During the flight I noticed that my seat partner still had the label sewn on the left arm of his new suit. Because he didn't seem to want to talk, I respected his privacy and didn't tell him about the label.

Now I wonder if I should have told him about his label. Abby, what should I have done?

- Southern Belle

DEAR SOUTHERN BELLE: Because your seat partner was not inclined to talk, you should have done exactly what you did - which was keep quiet.

The label on his jacket may not have been there because of an oversight. Some designers put their labels on the outside rather than the inside, so wearers can publicize not only the brand they are wearing but the implied price they paid for the garment. DEAR ABBY: How do you respond to a woman who is nearly 50 but acts like a child in public at meals? My sister-in-law, "Heather," who is divorced, will hum very loudly and sing out at the table. The family just smiles and says something about how she must really like the song.

Abby, it's embarrassing! We've been in very expensive restaurants, and Heather is rocking and saying, "La, la, la" loudly, and people ask if she's impaired. What can I do? I cringe at any public event.

- Red-Faced in Vero Beach, Fla.

DEAR RED-FACED: Heather may be making a bid for attention, which should strike you as more sad than embarrassing. Or she could have a mild form of Tourette's syndrome. Someone in the family - not you - should speak to her about it. *