Font.HasCharacter  

// Detects if the current font of a 3D text
// supports '-' sign
private var t : TextMesh;
function Start() {
    t = transform.GetComponent(TextMesh);
    if (t.font.HasCharacter("-"[0])) {
        Debug.Log("Font supports '-' sign.");
    } else {
        Debug.LogWarning("This font doesnt support '-'");
    }
}

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    private TextMesh t;
    void Start() {
        t = transform.GetComponent<TextMesh>();
        if (t.font.HasCharacter("-"[0]))
            Debug.Log("Font supports '-' sign.");
        else
            Debug.LogWarning("This font doesnt support '-'");
    }
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    private t as TextMesh

    def Start():
        t = transform.GetComponent[of TextMesh]()
        if t.font.HasCharacter('-'[0]):
            Debug.Log('Font supports \'-\' sign.')
        else:
            Debug.LogWarning('This font doesnt support \'-\'')