If a girl received flowers (like a bouquet, not just a single flower) while I was working with them, I'd immediately wonder what the guy did wrong (terrible first thought, but it's true).
Really? That's sad that you automatically think negative things about people rather than positive. I generally think: birthday, random I love you, anniversary, etc. when I see other people with them at work.
My husband once got me a huge bouquet of roses at work, a bit after we first started dating and he had to travel to Italy for work with a vacation in Italy afterwards. It's the only time he's done it, he claims because he knew we were something special and he didn't want me to feel neglected early in on our relationship while he was gone (also said the first I love you at the airport before flying out). I don't encourage him to buy me flowers (particularly overpriced Valentine's Day flowers!), but I still have that special bouquet dried, saved and displayed at our house 6+ years later.
For a super awkward moment...I got flowers once at work for my birthday which were unsigned. Call my then-bf to thank him (since my parents don't do that sort of thing) and discovered it wasn't him. After a bit of speculation, figured out it must have been an ex from 6 months ago. We were headed away that weekend, so it was also pretty poor timing on getting them too.