I am faurly sure that this is an aircraft part. I enclose some data on De Havilland parts numbers and for me it is the DHP in the circle as this would seem to be an inspectors stamp. I suggest you try one of the aviation forums.
It was not the norm for de Havilland to prefix part numbers with the letters DH. In the early years of Stag Lane design all drawings were numbered in a single numerical sequence. This covered types such as the DH 60 series, through to the Tiger Moth (DH 82) and Fox Moth (DH 83) etc. From memory, I think it was perhaps the Dragon (DH 84) which introduced a model designator in the drawing number but I would have to check if that is correct. Thus, the first element of the drawing (or part) number denoted the model, followed either by the drawing number or (for later types) a system designator and then a drawing number.
Thus, the configuration of de Havilland part numbers for the Chipmunk is C1-TP-313. This number denotes a Chipmunk part (C1) for the tailplane (TP). Other systems were denoted by letters such as CF (Controls, flap) and FS (fuselage, structure). Part numbers for the Dove and Devon start 104, the Heron 114, the Trident 121 etc. Strangely, de Havilland used to 'pick and mix' its parts and bits with Dove part numbers are still used on the Nimrod MRA4!
The early single numerical sequence of de Havilland drawings covered all types from the DH 60 to the DH 89 EXCEPT the DH 87.
For the DH 87 each part was designated by a three-digit prefix comprising a single digit followed by the Type number. The first digit was used to denote the location with the aircraft the part could be found. This system gave a much wider range of possible part numbers as the complexity of aircraft increased. The designation system for the DH 87 Hornet Moth followed this sequence:
687*** Engine installation
787*** Flying controls
At a late stage of Dragon Rapide/Dominie development the drawing sequence 989*** was introduced for parts used mainly in the various radio fits applied to the aircraft.
For the DH 90 to 93 inclusive, the same numerical designation system as for the DH 87 was used; ie;
190*** + 191*** + 192*** + 193*** - fuselage parts for the respective type. In some cases a 'zero' designator was used (ie 091***) for general arrangement drawings etc.
With the DH 94 the same system of designating part numbers by the aircraft type and its location on the aircraft was used but instead of using a single digit prefix to the type number, a letter suffix was used. For example:
94E*** Engine installation
94P*** Petrol and oil
This system then continued on subsequent aircraft types, with the letters after the type number being used more widely to discriminate between aircraft system; eg, on the Chipmunk:
C1-C******* Controls, flaps
C1-FS*** Fuselage, structure
As well as the type-specific drawing series, de Havilland used other generic designations:
DHA and DHS - used to denote de Havilland standard parts or processes applicable to more than one aircraft type.
J - used for standard material sections used across all types.
R - used for Repair drawings. For the early types using the original all-numeric drawing series the repair drawings were mixed up in a single R-series. Later models included R as a prefix to a number allocated in the normal drawing sequence; eg, from the Chipmunk RC1-FS*** would be a repair drawing for damage to the fuselage structure. As a slight complication, some repair drawings were prefixed RD - repair drawing - rather than R, as if the system was not complex enough already.
AN ADDENDUM BY BRUCE:
The DH thing is slightly out - on Mossie, the Letter is a prefix - ie L98 is a part of the engine system. Vampire is (eg) A00, but after Vampire it changes to the system shown for the Chipmunk.
Venom and subsequent Vampires can be a mix of the two.
Taken from David J Smiths 'High Ground Wrecks'.
'98' with a prefix letter denoting the location of the sub-assembly, followed by a four digit drawings number Odd numbers suggest a left hand part, even numbers suggest its complementary opposite hand part. i.e. A984131 is a fuselage component from the left side or as drawn.
A, B, C = fuselage
D, E, F = wings
G = undercarriage
J = tail unit
K = flying controls
L = engine installation
N = electrics
P = fuel
Q = hydraulics
R = radio
S = services
Z = misc