Bitcoin 

BTC

$17,456

 was up nearly 5% in 24 hours at the Wall Street open on March 25, but a new warning sign was giving traders cold feet.

Bitfinex whale flips to sell mode

Data from Cointelegraph Markets Pro and TradingView confirmed BTC/USD hitting multi-week highs of $45,137 on March 25 as Wall Street got underway.

As $45,000 reappeared for the first time since the start of the month, however, so did all-too-familiar behavior among some of Bitcoin's biggest investors.

Attention turned to exchange Bitfinex on the day, a platform famous for large-volume traders, or whales, guiding short-term price action with their trades.

As noted by popular trader Pentoshi, the entity that had purchased BTC at the last low near $34,000 had now put in a significant ask position beginning at $45,000.

Blockware lead insights analyst William Clemente agreed, telling Twitter users that it was now "popcorn time" for the market.

Cointelegraph contributor Michaël van de Poppe, meanwhile, flagged "a dozen" possible lower price targets should BTC/USD sweep liquidity at previous rejection points from March, these also lying just above $45,000.

"I'm not saying I'm bearish at this stage, but while we're making this build-up, I'm not really interested in longs at this point," he said in his latest YouTube update.

Only a rechallenge of $50,000, he added, would form the impetus to consider long positions.

"No longs" on Ethereum, says trade

Van de Poppe added that altcoins were also on the radar and that it would be interesting to see how Ether 

ETH

$1,336

, in particular, deals with upcoming resistance.

Related: What are the BTC price levels to watch as Bitcoin nears March peak?

The top ten cryptocurrencies by market cap showed clear copycat strength on daily timeframes, led by ETH/USD, which matched Bitcoin's 5% gains.

Cardano 

ADA

$0.316

, while dropping several percentage points on the day, was still up 35% compared to the same time last week, making it the top ten's best performer.