As a nerd who is a consultant in the fashion industry, I find myself walking into new situations and having to prove myself to people at all levels of a company (analyst programmers to CIOs) where how people look is their business. It's human nature to make snap judgements on initial appearances, so boldly wearing your favorite Shroedinger's cat joke T is probably not the best move. However, I believe there's a way to continue to show your nerd pride and keep your personal sense of style while continuing to fit in. A couple thoughts (not knowing whether the OP is male or female):
- Present yourself the way you want to be received. Look at the other directors and their attire. You don't have to dress as they do, but you do have to fit in somewhat. Their attire will give you the range you can work within. If they wear anything from business formal (suits and ties) to NY business casual (suit, no tie), you should work within that. Same is true if they're wearing anything from sweats to jeans. That's the range to work within.
- After determining the range, add your flair. If everyone's wearing black suits and white shirts and you don't dig the mortician look, buy a black suit with some texture or pinstripes. Add some color to the outfit with a shirt or tie or both. Get a different cut suit (e.g. English vs. Italian vs. American). Be careful not to stray too far, but find something that's more your style within the range set by your peers. You can show some nerd pride at this point too, but don't go crazy. If you're wearing a polo-style shirt, wear one with a TARDIS or alien head on the chest instead of a pony. Accessories can be playful like a a good, nerdy bracelet or watch (I wore a Disney Goofy watch that ran backwards for the first half of the 90s). Have fun with ties/scarves. There are ties that can fit in "the range" while being quite geek (no, fish or keyboard ties don't qualify here). In the end, if done right, your fellow geeks will notice. The nons won't. They'll think you're one of them.
- Dress for the day. Directors and managers are both leaders and doers. Some days, you'll be running with your staff. Some days, you'll be running with management. Know "the range" for each of these groups and dress to it. More often than not, you'll be running with both. In that case, dress to the management style.
- Alexander_686 is right. Clothes should be neat and well-fitting. Even the generic, business casual khakis and a button up look bad if they're unpressed, worn out, and hanging off you. Just because an office may be casual, doesn't mean you should be sloppy. Sloppy dressers aren't taken seriously by management. Don't show up in wrinkled clothing. Match your leathers (Whoever said "belts are always black" is wrong. Belts and shoes match. Generally handbags and small leather goods match your shoes too.). Shine your shoes, if they're supposed to be shined. Get a good haircut (not saying it has to be short or conservative).
- Feel good in what you wear. You may not be dressing entirely like you want because you're "playing the game" a little, but make it yours. There will be times you'll have to leave all the nerd at home and dress straight (e.g. interviews, meetings with your bosses boss, etc.). In those cases, a nice little tip I read years ago: Wear the wildest underwear under the most conservative outfit. You'll smile each time your reminded of your little secret.
One final thought: The good news is that the initial impression is just that. It's fleeting and only serves to give you the opportunity to prove yourself. Once you've proved yourself to the people around you, which you have since you're being promoted, it becomes less important what you wear (Keyword being *less*. Don't get sloppy!).