Mxsmanic wrote:

B, C, and D are easy, they have solid and dotted lines, as well as
numbers denoting lateral and vertical limits.

They are all easy to find on the chart, but I'm concerned about
finding them outside the window, without a GPS that shows them.

Without GPS:

Most B & C, and lots of D airports have a VORTAC on the field. DME
will tell you the distance from the DME station, which is usually near
the center of the field, and the airspace.. Otherwise, you need to
establish where you are using off-field VOR radials and/or chart denoted
visual landmarks. Easy landmarks include airports, roads (especially
intersections), cities, towers, stacks, power lines, water feature,
etc... I haven't flown with an NDB in a long time, so I can't comment
on using those.

This is taught, tested, and developed during training, and good pilots
put a lot of effort into location awareness. With practice, it becomes
easy, possibly second nature.

Typically, you wouldn't fly right up to the edge of sensitive airspace
unless you had a very high confidence in your position. If it's a
controlled airspace situation, you'd get clearance or establish two-way
communications, as required, while still obviously outside the space.
If I'm flying near, over, or under controlled airspace, I'll at least
monitor the frequency, and call if I'm near.

If the space is completely restricted, why poke at the beast? You'd
simply give it a reasonable, without-a-doubt cushion while passing by.