A few thoughts:
I personally think that geographic location might have something to do with all this.
While living in the D.C. area, there seemed to be almost relentless pressure (on one level) for everything to be free of all religious associations. (Even Easter weekend, which my county's government renamed "the Spring Holiday" - for one year, at least.)
But where I'm now living (not coincidentally, it's also where I grew up) is very, very different. Religion - Christianity, at least - is very much front and center, in the local newspaper, on radio, in the civic arena, etc. Although things have changed since I was a kid, it's striking (to me, at least) how much hasn't. And I would add that some of this is definitely cultural - this area is home to many people from Anabaptist denominations (Mennonites, Amish, Church of the Brethren, etc.) as well as being populated (mostly) by people of Scots-Irish (Irish Protestant, low-church) and German descent. Not surprisingly, there are a fair number of Catholics, but most Protestants seem to fall into the following categories:
- German Lutheran
- Scots-Irish and English Methodists and Presbyterians
- German Anabaptists
- some sort of "independent Bible church" or "independent 'Baptist'" affiliation
Driving in the country, you're pretty likely to pass small, plain signs with Bible verses (mostly put up by Mennonites) and, sometimes, barns and billboards with questions about where your soul is going to go when you die/when Jesus comes back. (I guess the latter are mostly sponsored by the various small, nondenominational Protestant churches.)
Church and Vacation Bible School and Sunday school are still important for a lot of people if for no other reason than that they're an outlet for socializing and, well, entertainment.
As for places like D.C., I think the secularism is largely superficial. There are thousands of churches in the D.C. metro area, along with many synagogues, mosques, Buddhist temples and shrines, Mormon stakes (and a very large Mormon temple), etc.
Clearly, the civil arena is pretty secular, but there's this whole other level on which many, many people are somehow hooked up to religious organizations and congregations, even if they only consider themselves to be part of X religion because they were raised that way (but don't follow the religion themselves), or because they married someone who is of Y religion and decided to convert, or... And that's not even counting all the groups that have no "official" organization (various kinds of pagan and neo-pagan groups, Wiccans, people who practice various animist and/or spiritist religions, etc.)
I know it seems like the US has become extremely secular, but I'm not at all convinced that that's true on a more than superficial level.
Certainly religion still plays an important role in America, and there are obvious outward signs (sometimes the literal signs that you mention) of its relevance. But in the context of the article that was originally quoted -- a humanist father who is concerned for his son, and about the religious messages he may receive -- I still think he has nothing to worry about.
Here's a surefire method that will guarantee success:
1) Send the kid to public schools for the first twelve years of his education. State/non-religious colleges are probably a good idea, too.
2) Buy a cable TV package, and ensure that the kid has a steady diet of MTV, E, and Bravo.
3) Make sure the kid is aware of/exposed to the latest pop hits and movies, particularly those geared toward teen/young adult audiences.
3) Let the kid hang out with the neighborhood kids, who will be exposed to the same influences noted above.
He's as good as gold.
Kids don't take their cues from billboards. They take them from their friends, their teachers, and the popular culture that surrounds them. And short of supernatural intervention, which can and does happen, I'm fairly certain that a thorough immersion in modern American culture will produce a fine consumer/hedonist who rejects religious beliefs, focuses exclusively on humans and their values, capacities, and worth, and believes that Christians are a silly, superstitious, and bigoted lot. The billboards and other ephemera will be quickly forgotten, or held up as examples for mockery and derision.
I realize that sounds dire, and it probably sounds peculiar coming from someone who makes part of his living by extolling the value of some elements of popular culture. Nevertheless, it's true. It's easier than it's ever been to raise a good humanist. It's the default cultural setting in America. Try comparing and contrasting Jesus, who calls us to take up our crosses and follow Him, with Britney Spears and Johnny Depp. Jesus doesn't stand a chance.