Yeah, what those guys said. At the casinos
where I've played it's mandatory to verbally announce a raise, and if you push additional chips into the pot without saying "raise," it's considered a call, no matter how many you put in.
As for style, I think it's best to use neatly-counted stacks, or to slide them in domino-style if you can keep them tidy while doing it. The dealers will often take apart a large stack to count them after you've pushed it in, so you may as well save them the trouble.
If you put your chips in too precisely other players might give you a hard time. I was once told I didn't need to be so "dainty" about putting my chips in the pot.