Do you mean something like this? ,
As far as I know, TeX is not really set up to do that sort of thing, and you have to resort to messy improvisations. I once had to construct a macro for putting a circle round a number, and even that isn't straightforward. It would produce results like . But at least TeX provides a circle symbol. If you want an oval then you have to be creative. I constructed those above by overlapping the set inclusion symbols and . That can sometimes be stretched to cover three letters, but there is a danger of a gap appearing, as in .
The implementation of TeX in this Forum does not allow the use of macros, so I have had to write out the construction in full each time. You can click on the results to see the code.