Sigil of Thanatos
From Tardis Wiki, the free Doctor Who reference
The Sigil of Thanatos was the sign of the super weapon Thanatos. It was similar in appearance to a stylised "s" with a vertical line through it.
Colonel Snathe had the Sigil of Thanatos tattoo onto his chest to remind him of what he searched for. (DWM: The Betrothal of Sontar)
