I say

I say, what is the meaning of this?

Adrian thought it worth while to try out his new slang. ‘I say, you fellows, here's a rum go. Old Biffo was jolly odd this morning. He gave me a lot of pi-jaw about slacking and then invited me to tea. No rotting! He did really.’

1991, Stephen Fry, chapter III, in The Liar, London: William Heinemann, →ISBN, page 26

[…] an excited gentleman […] pounded with the knocker on the door of No. 9. As someone did not appear with the instantaneity of a jack-in-the-box, he proceeded to repeat the summons, interspersing it with an occasional "I say!" shouted through the letter-box.

1923, Ernest Bramah [pseudonym; Ernest Brammah Smith], “(please specify the page)”, in The Eyes of Max Carrados, London: Grant Richards, →OCLC

When such men as Mr. Burke, Mr. Dundas, Mr. Pitt, Mr. Windham, and my Lord Grenville: when such men as these unreservedly and repeatedly avowed their sentiments on the condition of the Slave; when they saw no danger in the avowal; […] when, I say, these men thus thought, spoke, and acted […]

1823, William Wilberforce, Appeal to the Religion, Justice and Humanity of the Inhabitants of the British Empire in Behalf of the Negro Slaves in the West Indies

But when Amelia came down with her kind smiling looks (Rebecca must introduce her to her friend, Miss Crawley was longing to see her, and was too ill to leave her carriage)—when, I say, Amelia came down, the Park Lane shoulder-knot aristocracy wondered more and more that such a thing could come out of Bloomsbury; […]

1847 January – 1848 July, William Makepeace Thackeray, chapter 63, in Vanity Fair […], London: Bradbury and Evans […], published 1848, →OCLC