"two upon ten" meaning in English

{
  "etymology_text": "From the idea of keeping one's two eyes fixed on the shoplifter's ten fingers.",
  "head_templates": [
    {
      "args": {
        "1": "en",
        "2": "phrase"
      },
      "expansion": "two upon ten",
      "name": "head"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "phrase",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "English entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "English entries with topic categories using raw markup",
          "parents": [
            "Entries with topic categories using raw markup",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "English terms with non-redundant non-automated sortkeys",
          "parents": [
            "Terms with non-redundant non-automated sortkeys",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "topical",
          "langcode": "en",
          "name": "Ten",
          "orig": "en:Ten",
          "parents": [
            "Numbers",
            "All topics",
            "Terms by semantic function",
            "Fundamental"
          ],
          "source": "w"
        },
        {
          "kind": "topical",
          "langcode": "en",
          "name": "Two",
          "orig": "en:Two",
          "parents": [
            "Numbers",
            "All topics",
            "Terms by semantic function",
            "Fundamental"
          ],
          "source": "w"
        }
      ],
      "glosses": [
        "A coded warning among shopkeepers that a potential shoplifter must be watched."
      ],
      "id": "en-two_upon_ten-en-phrase-vmf~eDif",
      "links": [
        [
          "shopkeeper",
          "shopkeeper#English"
        ],
        [
          "shoplifter",
          "shoplifter#English"
        ]
      ],
      "synonyms": [
        {
          "word": "two on ten"
        }
      ]
    }
  ],
  "word": "two upon ten"
}

{
  "etymology_text": "From the idea of keeping one's two eyes fixed on the shoplifter's ten fingers.",
  "head_templates": [
    {
      "args": {
        "1": "en",
        "2": "phrase"
      },
      "expansion": "two upon ten",
      "name": "head"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "phrase",
  "senses": [
    {
      "categories": [
        "English entries with incorrect language header",
        "English entries with topic categories using raw markup",
        "English lemmas",
        "English multiword terms",
        "English phrases",
        "English terms with non-redundant non-automated sortkeys",
        "en:Ten",
        "en:Two"
      ],
      "glosses": [
        "A coded warning among shopkeepers that a potential shoplifter must be watched."
      ],
      "links": [
        [
          "shopkeeper",
          "shopkeeper#English"
        ],
        [
          "shoplifter",
          "shoplifter#English"
        ]
      ]
    }
  ],
  "synonyms": [
    {
      "word": "two on ten"
    }
  ],
  "word": "two upon ten"
}