The Australian-English phrase a thumbnail dipped in tar, and its variants, refer to rough penmanship.

This phrase occurs, for example, in the following from Park Watch (Melbourne, Victoria) of June 1999:

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Help us to keep Park Watch current and relevant by contributing items that you would like to see published.
Whether it’s recipes for bushwalkers, cartoons (like Roland Harvey’s, shown here), photos from your last bushwalk, or a few random thoughts jotted down with the proverbial thumbnail dipped in tar*…
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* And transcribed into legible type, as per the ‘Guidelines for Contributors’ of course!

The phrase a thumbnail dipped in tar, and its variants, allude to Clancy of the Overflow (1889), by the Australian poet ‘Banjo’ Paterson (Andrew Barton Paterson – 1864-1941).

This is the poem, as it was originally published in The Bulletin (Sydney, New South Wales) of Saturday 21^st December 1889:

“Clancy of the Overflow.”
[For The Bulletin.]

I had written him a letter which I had, for want of better
Knowledge, sent to where I met him down the Lachlan, years ago,
He was shearing when I knew him, so I sent the letter to him,
Just “on spec,” addressed as follows, “ Clancy, of ‘The Overflow.’”

And an answer came directed in a writing unexpected,
(Which I think the same was written with a thumb-nail dipped in tar)
’Twas his shearing mate who wrote it, and verbatim I will quote it:
“Clancy’s gone to Queensland droving, and we don’t know where he are.”

In my wild erratic fancy visions come to me of Clancy
Gone a-droving “down the Cooper” where the Western drovers go;
As the stock are slowly stringing, Clancy rides behind them singing,
For the drover’s life has pleasures that the townsfolk never know.

And the bush hath friends to meet him and their kindly voices greet him
In the murmur of the breezes and the river on its bars,
And he sees the vision splendid of the sunlit plains extended,
And at night the wond’rous glory of the everlasting stars.

I am sitting in my dingy little office, where a stingy
Ray of sunlight struggles feebly down between the houses tall,
And the fœtid air and gritty of the dusty, dirty city
Through the open window floating, spreads its foulness over all.

And in place of lowing cattle, I can hear the fiendish rattle
Of the tramways and the ’busses making hurry down the street,
And the language uninviting of the gutter children fighting,
Comes fitfully and faintly through the ceaseless tramp of feet.

And the hurrying people daunt me, and their pallid faces haunt me
As they shoulder one another in their rush and nervous haste,
With their eager eyes and greedy, and their stunted forms and weedy,
For townsfolk have no time to grow, they have no time to waste.

And I somehow rather fancy that I’d like to change with Clancy,
Like to take a turn at droving where the seasons come and go,
While he faced the round eternal of the cash-book and the journal—
But I doubt he’d suit the office, Clancy, of “The Overflow.”

BANJO.

The earliest occurrence that I have found of the phrase a thumbnail dipped in tar used without explicit reference to Andrew Barton Paterson’s poem is from the column Sunbeams, published in The Sun (Kalgoorlie, Western Australia) of Sunday 29^th September 1901:

The indenture system is not slavery, so the northern squatters and their friends aver. But it is a wonderfully good imitation. Before us, forwarded by the courtesy of some Carnavon reader, lies an “agreement” entered into on August 2, 1899, between Forrest and Burt, pastoralists, and Junnerin Yana, aboriginal native. The [illegible three-letter word], whose signature, of course, is of the “X his mark” variety, binds himself to serve his employers for the term of 12 months (thereby rendering himself liable to flogging and imprisonment should he break his so-called “contract”), while Forrest and Burt, on their part, covenant to supply their sl— servant—with sufficient food, a shirt, a pair of trousers, a blanket, and medicines and medical attendance when practicable and necessary, “unless the illness of Junnerin Yana is caused by his own improper act or default.” The last clause seems to cover the contingency of Junnerin being flogged within an inch of his life for insubordination. The document is endorsed by a police constable, who appears to have used a “thumbnail dipped in tar” for writing purposes, and who certifies that Junnerin “appears” to be 14 years old, “appears” to understand the contents of the document, and “appears” to be under no fear, coercion, or restraint. Fancy mere boys and girls being handed over body and soul to the tender mercies of ruffians like Brockman, De Pledge, or the Andersons, on the strength of this travesty of a contract!