This article argues that most of the inscribed objects (seals, miniature-tablets etc.) of ancient Indus valley civilization were essentially administrative-commercial tools (tax-tokens, trade-licences, metrological records, etc.) used for controlling the complex trading economy spread across the Indus settlements. It also argues that the inscriptions logographically encoded a commercial sublanguage to convey information about kinds of taxes/tithes, tax-receiving entities; tax-rates and modes; and activities (such as cultivation, manufacture, and trading of specific commodities) that these taxes covered and authorized. Building on the functional classification of Indus logograms performed in the author's previous structural analysis of Indus inscriptions and analysing various script-internal, archaeological, historical and linguistic evidence, this article seeks to interpret the semantic functionalities of different sign-classes. It proposes that: i) The numerical and metrological signs were used to represent certain tax-collection rates fixed for certain commodities, whereas the lexeme-signs following them ( ) represented those taxed commodities. ii) The Crop-signs ( ) represented different harvested grain-based taxes. iii) The phrase-final/terminal logograms ( ) encoded certain metrological modes (volumetric, weight-based, reed-measure-based etc.) of tax-collection, and thus metonymically encoded certain broad tax-categories. iv) The lexeme-signs appearing in the initial parts of the grammatically complex inscriptions ( ) represented the tax-collector entities and purpose of tax-payment. v) The signs mostly occurring in pre-phrase-final positions ( ) represented the mode of tax-payments through predefined equivalencies. vi) The bird-like logograms ( ) represented different precious stones including lapis lazuli, cornelian, agate etc.; while the fish-like logograms ( ) signified different apotropaic "fish-eye-beads", which were one of the most precious exported Indus commodities, coveted in ancient Near East. Analysing the related lexical roots of such commodities— e.g. ivory ("piru"); lapis lazuli whose colour was compared to the iridescent pigeon-neck ("kāsaka hya kapautaka"); and "eye-beads" (maṇi), in Mesopotamian lexicons, Amarna letters, ancient texts in Old-Persian language, BMAC languages, Sanskrit, Pali, Tamil etc. — this study claims that such words had originated in the Indus valley, and had spread to the languages of other civilizations through trade networks. Tracing out more such ancient metrological and revenue related terminologies (droṇa, bhāra, kṛṣṇala, raktikā, śara etc.) this study finally offers decipherment of a few Indus inscriptions.