Green’s Dictionary of Slang

1. (UK Und.) a warrant for arrest, search etc.

1935		Thieves Slang ms list from District Police Training Centre, Ryton-on-Dunsmore, Warwicks 12: W: Warrant.
c.1951		N. Algren ‘Watch Out for Daddy’ in Entrapment (2009) 131: Without a penny, without a friend. And a W on my forehead.
1956		N. Algren Walk on the Wild Side 67: ‘I got a W on me, Jack.’ ‘I’ll see the law-folks don’t snatch you, Kitty.’.
1958		F. Norman Bang To Rights 167: But if I don’t go [to the parole officer] they put a W out for me then I’ll get nicked again.
1977		D. Powis Signs of Crime 206: ‘W’, a A warrant to arrest or search.
1984		‘Derek Raymond’ He Died with His Eyes Open 71: If you do find there’s a W out for you, it could be because you wouldn’t cooperate with me.

2. a win.

1970		J. Bouton Ball Four 166: [W]e won 10-9 and I ended up with my first big W, as we baseball players call it.
2001		D. Jenkins Money-Whipped Steer-Job 205: I was happy for Buddy Stark, grabbing himself a W like that, his first victory of the year.
2008		W.D. Myers Game 193: [I]t was too late to cop the W and too late for the big comeback.

3. (US) something first-rate, excellent.

2017

femalenetwork.com 23 May 🌐 W (pronounced as /dub/) [...] means to catch a win. It's the antithesis of L or a loss. How to use it: "That deal is such a W! Get it before anyone does! ".