It is common practice for a casino in UK or Europe to hand out plaques at the cage where a player is drawing $$, rather than chips.
I think it is mainly for accountability purposes.
If I wish to either take a marker against my credit line (I wish ) , draw cash on a card, or exchange foreign currency, I will be paid in plaques. I take those plaques to a table and exchange them for chips. The dealer then drops the plaques down the same slot as he does banknotes. I cannot 'play' those plaques. In fact, if I were to place one on a roulette layout, then rather than exchanging it for chips as he would if I placed a £50 note (in Europe - 'cash' always plays, unlike the US), he will remove it, place it on the rim of the wheel and announce "change only, after this spin".

Some casinos (probably very few nowadays) have plaques with equal playable status as chips, generally for baccarat and its variants. To distinguish between the two types of plaques, you may encounter various difference. e.g.

Plain plaques for markers, striped plaques as playable pieces.
Non-negotiable plaques for markers, unendorsed plaques as playable pieces.
Oval plaques for markers, rectangular as playable pieces.

Some casinos may even have a combination of the above. Curzon House and Crockfords in London utilised a whole range of different pieces at the same time. If you followed the history of John Aspinall that I provided elsewhere, you will see that one of his gambling motives was to bring chemin-de-fer to the UK, so that the aristocracy (his clients) did not have to disappear to the south of France every winter to play. Because it was tradition to use plaques for chemmy in France, those larger casinos which were his earliest UK ventures also adopted their use.

The famous chemmy houses of France - Riviera, Ruhl and Palm Beach in Cannes, plus the Monte Carlo casinos, are generally those where you see the variants in plaques I have described above.
Bear in mind the sums of money being played for back then were relatively huge - £1,000 or 10,000FF minimum bets on chemmy (equivalent to $10,000 today). The smaller denom plaques you encounter were merely to pay the commission (change) on winning banker bets.