It is the Stores part number (Vocab Number)
A quick internet search shows :
Marking will vary between chests as the stores code and TEL STG MK number change depending upon which mark of scope the rifle is equipped with. In this case it is the most common version, BA5885 for the No. 32 MK. 3 (or written as MK. III sometimes.) Many chests were repainted in service and will often be found in glossy green and have markings painted around or reapplied. Many have a yellow marking (solid circle or band) which may be a stores marking. As well one occasionally finds regimental markings, shipping marking and later, NATO stores numbers. Old markings are often painted out.
No.4 MK. I (T) Sniper Equipment Markings www.captainstevens.com