No restrictions on Notam also this
Signature Flight Support | London Luton Airport Night Noise Closures
Also looks like for 2019 only the really noisy aircraft will be banned at night
2019 RESTRICTIONS
Aircraft exceeding noise quotient QC1 standard will be ineligible for night-time slots during the summer of 2019.
Luton does not seem as busy as it was for biz jets so I guess parking is more of an issue as Signature lost use of an overnight apron.