Real estate agents say the three most important characteristics of a property are "location, location, location." Advertisers live by a similar rule, and that is "frequency." Potential customers don't really hear/see your message until the seventh time they've been exposed to it.
So if you're looking to promote enrollment in high school physics, I encourage you to make liberal use of the TAKE PHYSICS posters. Better yet, come up with your own; they'll likely be better than mine. (Unless you live way out on the cutting edge, though, I don't recommend designing a physics version of the old 'Expose Yourself to Art' campaign. Just throwing that out there. But if you do, please send me a copy!)
The American Association of Physics Teachers (AAPT) has designed a couple of nice posters and includes links to them on their Resources page.
One is "The Top 10 Reasons Why You Should Take Physics."
Another is "Seven Myths About High School Physics." OK, technically, that one is a brochure. But print its two sides big, connect them, and you've got a hugenormous poster.
I recommend downloading high-resolution versions of these and printing them to the biggest paper you can handle. I have an Epson 3880 (because I'm into photography), so I can print to 17" x 22" paper. Your school might have something capable of more than that.
Print them and post them. Be aware of the high-traffic areas at your school. Think like an advertiser! Get them out into locations where they'll be seen. Don't relegate them to the window of your own classroom. That's not where your market is! Be sure to post them in the guidance counselors' office, where students are often waiting around for their appointment. There they are, with nothing to do but sit around and read the posters on the wall.
One might reasonably wonder if advertising is the way to go. Does it make your program appear desperate? No one else is advertising, why are you? (See next article.) If you are happy with your enrollments as they are or are uncomfortable stepping on the toes that might be stepped on by your campaign (again, see the article below), advertising is not for you.
If you know of a better means to higher physics enrollments, please share your ideas in the comments. I will say that my own early efforts—making presentations to the chemistry classes and even mounting a sophisticated, "Ed McMahon-style" personalized direct mail appeal—had nowhere near the efficacy of my much simpler TAKE PHYSICS campaign.