NOUN (3)

1. an arrowhead mark identifying British government property;

2. a mark shaped like an arrowhead; used to mark convicts' clothing;

3. an arrow with a wide barbed head;

The Collaborative International Dictionary of English v.0.48:

Arrow \Ar"row\, n. [OE. arewe, AS. arewe, earh; akin to Icel.
   ["o]r, ["o]rvar, Goth. arhwazna, and perh. L. arcus bow. Cf.
   Arc.]
   A missile weapon of offense, slender, pointed, and usually
   feathered and barbed, to be shot from a bow.
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   Broad arrow.
   (a) An arrow with a broad head.
   (b) A mark placed upon British ordnance and government
       stores, which bears a rude resemblance to a broad
       arrowhead.
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The Collaborative International Dictionary of English v.0.48:

Broad \Broad\ (br[add]d), a. [Compar. Broader
   (br[add]d"[~e]r); superl. Broadest.] [OE. brod, brad, AS.
   br[=a]d; akin to OS. br[=e]d, D. breed, G. breit, Icel.
   brei[eth]r, Sw. & Dan. bred, Goth. braids. Cf. Breadth.]
   1. Wide; extend in breadth, or from side to side; -- opposed
      to narrow; as, a broad street, a broad table; an inch
      broad.
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   2. Extending far and wide; extensive; vast; as, the broad
      expanse of ocean.
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   3. Extended, in the sense of diffused; open; clear; full.
      "Broad and open day." --Bp. Porteus.
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   4. Fig.: Having a large measure of any thing or quality; not
      limited; not restrained; -- applied to any subject, and
      retaining the literal idea more or less clearly, the
      precise meaning depending largely on the substantive.
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            A broad mixture of falsehood.         --Locke.
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   Note: Hence:
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   5. Comprehensive; liberal; enlarged.
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            The words in the Constitution are broad enough to
            include the case.                     --D. Daggett.
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            In a broad, statesmanlike, and masterly way. --E.
                                                  Everett.
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   6. Plain; evident; as, a broad hint.
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   7. Free; unrestrained; unconfined.
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            As broad and general as the casing air. --Shak.
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   8. (Fine Arts) Characterized by breadth. See Breadth.
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   9. Cross; coarse; indelicate; as, a broad compliment; a broad
      joke; broad humor.
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   10. Strongly marked; as, a broad Scotch accent.
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   Note: Broad is often used in compounds to signify wide,
         large, etc.; as, broad-chested, broad-shouldered,
         broad-spreading, broad-winged.
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   Broad acres. See under Acre.

   Broad arrow, originally a pheon. See Pheon, and Broad
      arrow under Arrow.

   As broad as long, having the length equal to the breadth;
      hence, the same one way as another; coming to the same
      result by different ways or processes.
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            It is as broad as long, whether they rise to others,
            or bring others down to them.         --L'Estrange.
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   Broad pennant. See under Pennant.
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   Syn: Wide; large; ample; expanded; spacious; roomy;
        extensive; vast; comprehensive; liberal.
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WordNet (r) 3.0 (2006):

broad arrow
    n 1: an arrowhead mark identifying British government property
    2: a mark shaped like an arrowhead; used to mark convicts'
       clothing
    3: an arrow with a wide barbed head