A couple of months ago I started noticing a co-worker who works in a different department. He works in a visitor relations job in a public outside area where I usually go during breaks to make personal calls (I don't get cell reception anywhere else). For a few weeks I noticed him looking at me quite often, and at first didn't think anything of it, but then realized that I was interested in him. We've never had a conversation but I know he's 31 (I'm 27) and I'm 99% sure he's single. Unfortunately we have different work hours so I don't see him in the parking lot or lunch room, and I work in a secure area that his department doesn't have access to (there's no interaction between our departments). We do usually take afternoon breaks outside around the same time so that would probably be the best opportunity to start a conversation.

Sorry for the length of the post, but what I'm asking is what's the best way to show a guy you're interested? I've spent the last several years focusing on academics and my career, so I'm a little rusty at this. Any suggestions on how to show him I'd like to get to know him better?

Don't be subtle because us guys are not always great at picking up on hints. Strike up a conversation. Just go up to him say hi I'm your name and I think your cute would you like to go get coffee sometime. Most guys like a girl who is straight forward and he will most likely be very flattered and surprised that you were so blunt and say yes.

Lol I know how u feel well just start talking to him and say hey didn't we already meet and that will start a convesation

Bad
Couse he mught be freaked out

Next time you see him, just introduce yourself. Something like, "I often see you when I'm on break but I don't think we've actually met - I'm Ashley - I work in accounting". I think it's a mistake to start by telling him he's cute or to ask him out - just make an introduction, and put the ball in his court. More than that would be weird if he isn't interested back in you - a lot of guys look even if they are dating someone else, so that's not enough to go on. And you don't want to be too bold, get shut down and then have to work with him and see him all the time... an introduction is encouraging without going overboard.