This pictorial motif gets normalized in Indus writing system as a hieroglyph sign.

Variants of Sign 48

कर्णक m. (ifc. f(आ).) a prominence or handle or projection on the side or sides (of a vessel &c ) , a tendril S3Br. Ka1tyS3r. rebus: कारणिक, कर्णिक investigating, scribe, supercargo, steersman. baraḍo =spine; backbone (Tulu) Rebus: baran, bharat 'mixed alloys' (5 copper, 4 zinc and 1 tin) (Punjabi); Associatedwith FS 83: Dotted circledhāvaḍ 'smelter' 

Dotted circle as Indus Script hypertext  धावड dhāvaḍa 'red ferrite ore smelter'.

The hypertext is composed of two hieroglyphs: dot + circle. The dot is a stylized dhāī˜ (Lahnda) which signifies a single strand of rope or thread.

1. dhāv 'throw of dice' rebus: dhāū, dhāv 'mineral' 2. vaṭṭa 'circle' rebus:  vaṭṭa 'revenue division' as in: vaṭṭa-maṇiyam, n. < வட்டம் +. The office of revenue collection in a division.

Thus, together the rebus reading is: धावड dhāvaḍa 'red ferrite ore smelter'

धाव (p. 250) dhāva m f A certain soft, red stone. Baboons are said to draw it from the bottom of brooks, and to besmear their faces with it.  धवड (p. 249) dhavaḍa m (Or धावड) A class or an individual of it. They are smelters of iron. धावड (p. 250) dhāvaḍa m A class or an individual of it. They are smelters of iron. धावडी (p. 250) dhāvaḍī a Relating to the class धावड. Hence 2 Composed of or relating to iron. 

वृत्त [p= 1009,2] mfn. turned , set in motion (as a wheel) RV.; a circle; vr̥ttá ʻ turned ʼ RV., ʻ rounded ʼ ŚBr. 2. ʻ completed ʼ MaitrUp., ʻ passed, elapsed (of time) ʼ KauṣUp. 3. n. ʻ conduct, matter ʼ ŚBr., ʻ livelihood ʼ Hariv. [√vr̥t1] 1. Pa. vaṭṭa -- ʻ round ʼ, n. ʻ circle ʼ; Pk. vaṭṭa -- , vatta -- , vitta -- , vutta -- ʻ round ʼ; L. (Ju.) vaṭ m. ʻ anything twisted ʼ; Si. vaṭa ʻ round ʼ, vaṭa -- ya ʻ circle, girth (esp. of trees) ʼ; Md. va'ʻ round ʼ GS 58; -- Paš.ar. waṭṭəwīˊk, waḍḍawik ʻ kidney ʼ ( -- wĭ̄k vr̥kká -- ) IIFL iii 3, 192?(CDIAL 12069) வட்டம்போர் vaṭṭam-pōr, n. < வட்டு +. Dice-play; சூதுபோர். (தொல். எழுத். 418, இளம்பூ.) வட்டச்சொச்சவியாபாரம் vaṭṭa-c-cocca-viyāpāram, n. < id. + சொச்சம் +. Money-changer's trade; நாணயமாற்றுமுதலியதொழில். Pond. வட்டமணியம் vaṭṭa-maṇiyam, n. < வட்டம் +. The office of revenue collection in a division; வட்டத்துஊர்களில்வரிவசூலிக்கும்வேலை. (R. T.) వట్ట (p. 1123) vaṭṭa vaṭṭa. [Tel.] n. The bar that turns the centre post of a sugar mill. చెరుకుగానుగరోటినడిమిరోకలికివేయుఅడ్డమాను. వట్టకాయలు or వట్టలు vaṭṭa-kāyalu. n. plu. The testicles. వృషణములు, బీజములు. వట్టలుకొట్టు to castrate. lit: to strike the (bullock's) stones, (which are crushed with a mallet, not cut out.) వట్ర (p. 1123) vaṭra or వట్రన vaṭra. [from Skt. వర్తులము.] n. Roundness. నర్తులము, గుండ్రన. వట్ర. వట్రని or వట్రముగానుండే adj. Round. గుండ్రని.

The + glyph of Sibri evidence is comparable to the large-sized 'dot', dotted circles and + glyph shown on this Mohenjo-daro seal m0352 with dotted circles repeated on 5 sides A to F. Mohenjo-daro Seal m0352 shows dotted circles in the four corners of a fire-altar and at the centre of the altar together with four raised 'bun' ingot-type rounded features. Rebus readings of m0352 hieroglyphs:

Ivory tablets Mohenjodaro with dotted circles PLUS duck: vartaka 'duck' rebus: vartaka 'merchant'.

On the Harappa tablet, the three signs from the left on side a occur most frequently in the corpora and relate to metalwork.

Harappa. Prism tablet. H94-2177/4999-01: Molded faience tablet, Period 3B/3C. Rebus reading:

Two 'ingot' hieroglyphs: dul ḍ̠aḇ 'cast ingot'

'Backbone' hieroglyph:karaṁḍa ʻbackboneʼ Rebus: karaḍa 'hard alloy'

'crocodile' hieroglyph: kāru 'crocodile' (Telugu) Rebus: kāruvu 'artisan' (Telugu) khār 'blacksmith' (Kashmiri)

'two' hieroglyph + 'rimless pot' hieroglyph: dula 'two' Rebus: dul 'cast metal' + baṭa'rimless pot' Rebus: baṭa 'furnace'. Thus metal-casting furnace.