Check if a string contains one of 10 characters

The following would be the simplest method, in my view:

var match = str.IndexOfAny(new char[] { '*', '&', '#' }) != -1

Or in a possibly easier to read form:

var match = str.IndexOfAny("*&#".ToCharArray()) != -1

Depending on the context and performance required, you may or may not want to cache the char array.

As others have said, use IndexOfAny. However, I'd use it in this way:

private static readonly char[] Punctuation = "*&#...".ToCharArray();

public static bool ContainsPunctuation(string text)
{
    return text.IndexOfAny(Punctuation) >= 0;
}

That way you don't end up creating a new array on each call. The string is also easier to scan than a series of character literals, IMO.

Of course if you're only going to use this once, so the wasted creation isn't a problem, you could either use:

private const string Punctuation = "*&#...";

public static bool ContainsPunctuation(string text)
{
    return text.IndexOfAny(Punctuation.ToCharArray()) >= 0;
}

or

public static bool ContainsPunctuation(string text)
{
    return text.IndexOfAny("*&#...".ToCharArray()) >= 0;
}

It really depends on which you find more readable, whether you want to use the punctuation characters elsewhere, and how often the method is going to be called.

EDIT: Here's an alternative to Reed Copsey's method for finding out if a string contains exactly one of the characters.

private static readonly HashSet<char> Punctuation = new HashSet<char>("*&#...");

public static bool ContainsOnePunctuationMark(string text)
{
    bool seenOne = false;

    foreach (char c in text)
    {
        // TODO: Experiment to see whether HashSet is really faster than
        // Array.Contains. If all the punctuation is ASCII, there are other
        // alternatives...
        if (Punctuation.Contains(c))
        {
            if (seenOne)
            {
                return false; // This is the second punctuation character
            }
            seenOne = true;
        }
    }
    return seenOne;
}