Hi There,
I had a groundschool and flew a civilian L-39 a couple of years ago. (Only 2 flights, unfortunately).
There are a few items of interest in that area of the nose. The warning placard and flag under the nose should be for the ejection seat contactor box. (Seat interlock). On military versions, the RSBN (Russian radio-nav set) and IFF radios are also in the nose along with their antennae. Which may account for the radioactivity symbol.
There is also an air pressure gauge on the nose for either O2 pressure or brake or pressurization accumulator, I can't remember which. There's also a little red and white post that sticks up on the nose in the pilots line of sight as a alternative way to confirm the nose gear is extended. There are similar posts on the wings for the main gear.
O And by the way, on the right side of the tail there are 4 colour flare launchers for lost or no-comm signalling. Just like the Ka-50!
This is a fantastic airplane! Built very solidly, very forgiving and a joy to fly.
Hope that helps!