No, you can't. You can only get the emblems when you prestige.
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If your talking about Modern Warfare 2, go to callsigns/killstreaks, and click Emblem. If your talking about Black Ops, go to player card, edit player card.
See related links.
2nd prestige
Ten Tactical Nukes to unlock the emblem.
It happens to be a title, not an emblem. You're supposed to get 25 kills with fragmentation grenades.