It's basically saying "Oi, you". But it's a rude way of saying it and can have very strong confrontational undertones. If a Yakuza type says it to you, then you're in deep shit.
(Note that Hiroshima dialect is also the stereotypical Yakuza dialect. So a lot of the more confrontational Hiroshimaben phrases can sound downright scary in certain contexts... because they might sound like the Yakuza is threatening you.)
The cultural equivalent would be kinda like saying "You wot mate?" in British English.
(Or "U wot m8", but that's the online parodied style usually only used for comedic effect.)
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You Tokyoites keep gabbing on about how us Osakans have a 'scary tone', don't 'ya!This 'ere Hiroshima-livin' girl, shes sayin'"Odorya"!Goddamned 'Odorya'!!That's the scary one, right!!
"Oi, you". Has confrontational undertones. You really don't want to hear a Yakuza type say it to you.